Unable to load DLL (Module could not be found HRESULT: 0x8007007E)

Question

I have a dll library with unmanaged C++ API code I need to use in my .NET 4.0 application. But every method I try to load my dll I get an error:

Unable to load DLL 'MyOwn.dll': The specified module could not be found. (Exception from HRESULT: 0x8007007E)

I have read and tried several solutions I have found on the internet. Nothing works..

I have tried using following methods:

[DllImport("MyOwn.dll",  CallingConvention = CallingConvention.Cdecl)]
[return: MarshalAs((UnmanagedType.I4))]
public static extern Int32 MyProIni(string DBname, string DBuser_pass,
    string WorkDirectory, ref StringBuilder ErrorMessage);

When I tried following this article and when I run this example (from the downloaded code) it runs without a problem (the dll used is in the bin/debug folder)

I have copied my dll (along with all the files the it depends on into my bin folder).

I also tried this approach but got the same error:

[DllImportAttribute(MyOwnLibDllPath, EntryPoint="TMproIni")]
[return: MarshalAs(UnmanagedType.I4)]
public static extern  int MyproIni(string DBname, string DBuser_pass, 
    string WorkDirectory, ref StringBuilder ErrorMessage);

Any suggestions?

Verbenia

Answer 1

From what I remember on Windows the search order for a dll is:

1. Current Directory
2. System folder, C:\windows\system32 or c:\windows\SysWOW64 (for 32-bit process on 64-bit box).
3. Reading from the Path environment variable

In addition I'd check the dependencies of the DLL, the dependency walker provided with Visual Studio can help you out here, it can also be downloaded for free: http://www.dependencywalker.com

Transhumance

found some dependency's missing (Oracle and some dll from IE). Need to install Oracle since my dll depends on that..then i will know :) Found the problem with DependencyWalker ;) – Verbenia

No worries, it's saved many hours of head scratching for me, great little tool! :-) – Transhumance

+1 to Keith Halligan for suggesting DependencyWalker. It told me that the not all the dependencies had the same CPU type (x86/x64). I copied all the files that had the same CPU type to my application's bin folder, and that resolved the problem. – Augustus

Every dll I can find on my system has DependencyWalker claiming that there's an error with different CPU types - even System.Web.Mvc.dll. There's some sort of false alarm here. – Leekgreen

In my case the problem was attempting to load a C++ DLL compiled for Debug. That needs the C++ debug runtime, which means you have to install Visual Studio. Or recompile the DLL for Release, and install the C++ runtime distributable. – Apollus

Answer 2

You can use the dumpbin tool to find out the required DLL dependencies:

dumpbin /DEPENDENTS my.dll

This will tell you which DLLs your DLL needs to load. Particularly look out for MSVCR*.dll. I have seen your error code occur when the correct Visual C++ Redistributable is not installed.

You can get the "Visual C++ Redistributable Packages for Visual Studio 2013" from the Microsoft website. It installs c:\windows\system32\MSVCR120.dll

In the file name, 120 = 12.0 = Visual Studio 2013.

Be careful that you have the right Visual Studio version (10.0 = VS 10, 11 = VS 2012, 12.0 = VS 2013...) right architecture (x64 or x86) for your DLL's target platform, and also you need to be careful around debug builds. The debug build of a DLL depends on MSVCR120d.dll which is a debug version of the library, which is installed with Visual Studio but not by the Redistributable Package.

Vexillum

adding the VS C++ redistributables was it for me! needed v10.0 (2010). Thanks mucho!!! – Curacy

Is there any way to tell whether 64-bit or 32-bit versions of the redistributables are required? – Fugger

dumpbin /ALL will tell you whether my.dll is x86 of x64 – Vexillum

For those who still suffers from this problem, if you use debug binary, the C++ runtime redistributables version needs to be exactly the same as where you built it. – Smilacaceous

@skyline75489's comment saved the day for me. C++ library worked just fine on my machine but failed to load everywhere else due to VS linking it to the debug version of msvcr. – Jagged

Answer 3

The DLL has to be in the bin folder.

In Visual Studio, I add the dll to my project NOT in References, but "Add existing file". Then set the "Copy to Output Directory" Property for the dll to "Copy if newer".

Inconsequential

this works for my case where I use JLinkArm.dll – Secretarygeneral

Answer 4

This is a 'kludge' but you could at least use it to sanity-test: Try hard-coding the path to the DLL in your code

[DllImport(@"C:\\mycompany\\MyDLL.dll")]

Having said that; in my case running dumpbin /DEPENDENTS as suggested by @anthony-hayward, and copying over 32-bit versions of the DLLs listed there into my working directory solved this problem for me.

The message is just a bit misleading, becuase it isn't "my" dll that can't be loaded - it's the dependencies

Wellbalanced

Answer 5

Try to enter the full-path of the dll. If it doesn't work, try to copy the dll into the system32 folder.

Semicolon

is it ok to have all dependency's in the System32 folder and my dll somewhere else? – Verbenia

Dependencies will also be searched as per windows dll search path order as specified by https://mcmap.net/q/151410/-unable-to-load-dll-module-could-not-be-found-hresult-0x8007007e – Desilva

You are not supposed to copy your own DLLs into System32 folder. That folder is reserved for system components such as runtimes, driver components, etc, not for random DLLs belonging to user applications. – Bluepoint

Answer 6

"Unable to load DLL 'xxx.dll': The specified module could not be found. (Exception from HRESULT: 0x8007007E)" means the file CAN be found BUT it's not able to load it. Try to copy the DLL file to the root folder of your application, some DLL libraries need to be available in the root folder of the application in order for it to work. Or check if there are any other depending DLL files required by it.

"Cannot find DLL 'xxx.dll': ..." means the file CANNOT be found. Try to check the path. For example, [DllImport(@"\Libraries\Folder\xxx.dll")]

Rosana

Thank you, very much for including the hex HRESULT. My exceptions were translated and this tiny textual difference was lost in translation (which makes it harder to search for) – Quintain

Thanks, this HRESULT: 0x8007007E was crucial information. I was wasting time with path settings when I should have been focused on other dlls that the not found dll was dependent on.. – Ivey

If this were true, I shouldn't get the error '0x8007007E' when I delete the DLLs. But I still get it. – Terle

Answer 7

Ensure that all dependencies of your own dll are present near the dll, or in System32.

Conjectural

Answer 8

There is one very funny thing (and has a technical relevance) which might waste your hours so thought of sharing it here -

I created a console application project ConsoleApplication1 and a class library project ClassLibrary1.

All the code which was making the p/invoke was present in ClassLibrary1.dll. So before debugging the application from visual studio I simply copied the C++ unmanaged assembly (myUnmanagedFunctions.dll) into the \bin\debug\ directory of ClassLibrary1 project so that it can be loaded at run-time by the CLR.

I kept getting the

Unable to load DLL

error for hours. Later on I realized that all such unmanaged assemblies which are to be loaded need to be copied into the \bin\debug directory of the start-up project ConsoleApplication1 which is usually a win form, console or web application.

So please be cautious the Current Directory in the accepted answer actually means Current Directory of main executable from where you application process is starting. Looks like an obvious thing but might not be so at times.

Lesson Learnt - Always place the unamanaged dlls in the same directory as the start-up executable to ensure that it can be found.

Below

This fixed things for me too. Feels kind of weird to put the DLLs in the main project instead of the project that's actually using them, though... – Psychosocial

@SeanDuggan that is because it is a "dynamic linking library" meaning that it is used (loaded) at run time as opposed to static libraries that are used at linking time. – Desantis

I have tried adding the dll into the bin\Debug and the obj\Debug directories and I keep getting the "Unable to load DLL" – Desantis

Answer 9

Turn on the fusion logging, see this question for lots of advice on how to do that. Debugging mixed-mode apps loading problems can be a right royal pain. The fusion logging can be a big help.

Untraveled

Answer 10

Make sure you set the Build Platform Target to x86 or x64 so that it is compatible with your DLL - which might be compiled for a 32 bit platform.

Specifically:

• compiled for 32 bit platform (x86)
• compiled for 64 bit platform (x64 or AMD64 or similar)

Also, as clarified in other answers - your DLL will need to reside in the correct folder on your machine depending on whether the DLL is 32bit or 64bit. (Also make sure any dependencies of the DLL are in the same folder as the DLL)

Binion

Answer 11

In my case one unmanaged dll was depending on another which was missing. In that case the error will point to the existing dll instead of the missing one which can be really confusing.

That is exactly what had happen in my case. Hope this helps someone else.

Calandracalandria

Answer 12

I had the same problem when I deployed my application to test PC. The problem was development PC had msvcp110d.dll and msvcr110d.dll but not the test PC.

I added "Visual Studio C++ 11.0 DebugCRT (x86)" merge module in InstalledSheild and it worked. Hope this will be helpful for someone else.

Dynamometry

You are not allowed to distribute debug CRT with your setup -- Microsoft license forbids that (and for a very good reason). Even the folder where it is stored is called debug_nonredist as in non-redistributable. – Bluepoint

Answer 13

If the DLL and the .NET projects are in the same solution and you want to compile and run both every time, you can right click the properties of the .NET project, Build events, then add something like the following to Post-build event command line:

copy $(SolutionDir)Debug\MyOwn.dll .

It's basically a DOS line, and you can tweak based on where your DLL is being built to.

Eloisaeloise

Answer 14

I got this error for one C++ project in our solution, and only on our buildmaster's machine. The rest of us could build it with no problem.

In our case it was because that particular project had <WindowsTargetPlatformVersion> in the .vcxproj file set to "10.0" vs. "10.0.18362.0" as in all our other C++ projects.

Not specifying the entire SDK version number seems to have allowed MSBuild to choose the newest(?) SDK and associated build tools.

Our buildmaster likely had the remnants of a newer SDK on his machine, and MSBuild was trying to use it (and thus RC.exe was not found).

In any case, bringing up the project's property page and changing Configuration Properties > General > Windows SDK Version to "10.0.18362.0" (or whichever specific version of the SDK you have installed) for all of the project's configurations/platforms did the trick.

Embodiment

Answer 15

I think your unmanaged library needs a manifest.
Here is how to add it to your binary. and here is why.

In summary, several Redistributable library versions can be installed in your box but only one of them should satisfy your App, and it might not be the default, so you need to tell the system the version your library needs, that's why the manifest.

Rivera

Answer 16

Setup: 32-bit Windows 7

Context: Installed a PCI-GPIB driver that I was unable to communicate through due to the aforementioned issue.

Short Answer: Reinstall the driver.

Long Answer: I also used Dependency Walker, which identified several missing dependency modules. Immediately, I thought that it must have been a botched driver installation. I didn't want to check and restore each missing file.

The fact that I was unable to find the uninstaller under Programs and Features of the Control Panel is another indicator of bad installation. I had to manually delete a couple of *.dll in \system32 and registry keys to allow for driver re-installation.

Issue fixed.

The unexpected part was that not all dependency modules were resolved. Nevertheless, the *.dll of interest can now be referenced.

Longeron

Answer 17

I have come across the same problem, In my case I had two 32 bit pcs. One with .NET4.5 installed and other one was fresh PC.

my 32-bit cpp dll(Release mode build) was working fine with .NET installed PC but Not with fresh PC where I got the below error

Unable to load DLL 'PrinterSettings.dll': The specified module could not be found. (Exception from HRESULT: 0x8007007E)

finally,

I just built my project in Debug mode configuration and this time my cpp dll was working fine.

Apish

Answer 18

Also faced the same problem when using unmanaged c/c++ dll file in c# environment.

1.Checked the compatibility of dll with 32bit or 64bit CPU.

2.Checked the correct paths of DLL .bin folder, system32/sysWOW64 , or given path.

3.Checked if PDB(Programme Database) files are missing.This video gives you ans best undestand about pdb files.

When running 32-bit C/C++ binary code in 64bit system, could arise this because of platform incompatibility. You can change it from Build>Configuration manager.

Despatch

Answer 19

I faced the same problem when import C++ Dll in .Net Framework +4, I unchecked Project->Properties->Build->Prefer 32-bit and it solved for me.

Brinton

Answer 20

It has nothing to do with dependencies if you checked all dependencies and you know you got them all, it has nothing to do with the file being in the wrong directory either or incorrect ARGUMENTS passed to dll, the DLL Fails to load using LoadLibrary itself.. you could check the address returned from LoadLibrary is always 0x0000000 (not loaded).

I couldn't figure this error out either it worked fine on Windows 7, but on Windows 10 it doesn't work. I fixed the problem though it had nothing to do with missing dependencies or Runtime redistributable packs.

The problem was I had to pack the DLL with upx and it started working again.

Something with the file being unpacked and compiled on old Windows XP operating system created a bad PE Header or Bad file format or something, but packing it with UPX did the trick works fine now and the DLL got 3x smaller haha.

Tabasco