The type or namespace name could not be found [duplicate]

Asked 21/1, 2011 at 23:36 Answered 15/10, 2014 at 2:56

Solved c#visual-studio-2010 reference using-statement using-directives

530

I have a C# solution with several projects in Visual Studio 2010. One is a test project (I'll call it "PrjTest"), the other is a Windows Forms Application project (I'll call it "PrjForm"). There is also a third project referenced by PrjForm, which it is able to reference and use successfully.

PrjForm references PrjTest, and PrjForm has a class with a using statement:

using PrjTest;

Reference has been correctly added
using statement is correctly in place
Spelling is correct
PrjTest builds successfully
PrjForm almost builds, but breaks on the using PrjTest; line with the error:

The type or namespace name 'PrjTest' could not be found (are you missing a using directive or an assembly reference?)

I've tried the following to resolve this:

Removed Resharper (since Resharper had no trouble recognizing the referenced project, I thought it might be worth a shot)
Removed and re-added the reference and using statement
Recreated PrjForm from scratch
PrjForm currently resides inside the PrjTest folder, I tried moving it to an outside folder
Loaded the solution on a different computer with a fresh copy of VS 2010

I have done my homework and spent far too long looking for an answer online, none of the solutions has helped yet.

What else could I try?

Coccus answered 21/1, 2011 at 23:36 Comment(10)

are you sure the PrjTest has a Namespace named PrjTest – Snowdrop 21/1, 2011 at 23:41

Wouldn't you know it: #4287099 Turns out this was a client profiling issue, I didn't even think to check for that.. – Coccus 21/1, 2011 at 23:45

@Shekhar_Pro: I'm sure, it was one of the first things I checked.. – Coccus 21/1, 2011 at 23:46

Yep... this is generally a .NET Framework incompatibility\mismatch thingy. The problem is that Visual Studio (even 2013) won't tell you that in the Error List output window. :( – Matrices 1/7, 2014 at 15:15

I've closed this as a duplicate because after careful reading your issue was the exact same one as the duplicate which pre-dates this question by 6 months. (Your issue was a client profile assembly referencing a full framework assembly). – Pretor 23/1, 2015 at 1:5

@slugster: I wish I had seen your answer a long time ago, it would have saved me a lot of trouble. I guess the trick is knowing the keywords to search for... – Coccus 30/1, 2015 at 23:5

I had the same issue in Visual Studio 2019, all I needed to do was to restart VS2019 and it worked. – Enid 20/11, 2019 at 13:45

Check in the .csproj file of that cs class that you might have changed recently. You need to push that. – Projectile 16/12, 2019 at 15:17

Spent a day trying to find a solution for this. Did everything I could think of and everything that the internet suggested to me. Nothing worked. Fixed it by restarting my PC. 🤯 – Tiloine 25/8, 2022 at 13:48

recently had this and it turned out I had two projects with the same name and had inadvertently referenced the wrong one while making a change. I quintuple checked the reference was good but was still missing types but it was because the types were in the other project. Took me a long time to realize there were two projects. – Fashionable 18/3 at 23:0

751

See this question.

Turns out this was a client profiling issue.

PrjForm was set to ".Net Framework 4 Client Profile" I changed it to ".Net Framework 4", and now I have a successful build.

Thanks everyone! I guess it figures that after all that time spent searching online, I find the solution minutes after posting, I guess the trick is knowing the right question to ask..

Coccus answered 21/1, 2011 at 23:52 Comment(10)

Same error, but in my case I was trying to use a 4.0 dll in a 3.5 project. – Myiasis 9/4, 2013 at 20:32

Same error, but here it was 4.5 dll in 4.0 project. – Coral 26/11, 2013 at 14:15

This happened to me last week but from loading a 4.5.2 library in a 4.5 project. Just a note: A 4.5.2 project can load a 4.5 or 4.5.1 library just fine. – Autotransformer 12/1, 2015 at 16:13

from where can I change the framework as you have described? – Tarry 14/4, 2016 at 6:44

@KinjanBhavsar: it's in the project properties – Coccus 14/4, 2016 at 16:52

Thank you! scratching my head for an hour! I accidentally added a 4.6.2 proj and not 4.5.2. – Tomi 11/9, 2016 at 13:22

In my case it was happening because the CS file was not properly added to the csproj. Re adding the class file to the project fixed the issue. – Anallise 4/9, 2018 at 15:9

learn.microsoft.com/en-us/dotnet/framework/deployment/… According to this "Starting with the .NET Framework 4.5, the Client Profile has been discontinued and only the full redistributable package is available. " – Limitative 12/9, 2018 at 19:4

could someone add a screen shot or a good description of how to change PrjForm in VisualStudio2017. I have looked at every tab in the project properties and I don't see anything remotely named that. – Victor 4/1, 2020 at 19:9

On my side I was needed to downgrade the project .NET version and it worked. Thanks for the inspiration. – Marindamarinduque 31/8, 2023 at 5:12

In my case I had:

Referenced DLL : .NET 4.5

Project : .NET 4.0

Because of the above mismatch, the 4.0 project couldn't see inside the namespace of the 4.5 .DLL. I recompiled the .DLL to target .NET 4.0 and I was fine.

Incoherent answered 28/11, 2012 at 4:1 Comment(1)

One of my projects was updated from 4.5 to 4.5.2 and triggered this issue.... – Frightfully 2/8, 2021 at 17:24

Another thing that can cause this error is having NuGet packages that have been built with a newer version of .NET.

The original error:

frmTestPlanSelector.cs(11,7): error CS0246: The type or namespace name 'DatabaseManager' 
could not be found (are you missing a using directive or an assembly reference?)

Further up in the log I found this:

C:\Windows\Microsoft.NET\Framework\v4.0.30319\Microsoft.Common.targets(1605,5): warning MSB3275: The primary reference "[redacted]\DatabaseManager\bin\Release\DatabaseManager.dll" could not be resolved because it has an indirect dependency on the assembly "System.Data.SQLite, Version=1.0.94.0, Culture=neutral, PublicKeyToken=db937bc2d44ff139" which was built against the ".NETFramework,Version=v4.5" framework. This is a higher version than the currently targeted framework ".NETFramework,Version=v4.0".

The solution was to re-install the NuGet packages:

http://docs.nuget.org/docs/workflows/reinstalling-packages

Detestation answered 15/10, 2014 at 2:56 Comment(2)

this did it for me, my app was targeting 4.5.2 but unit tests were on 4.5 thanks. – Therapsid 19/8, 2015 at 6:12

This one! I had shut off warnings because, you know, WARN... Turned that back on and it showed the error straight away. – Suppliant 27/6, 2018 at 19:10

PrjForm was set to ".Net Framework 4 Client Profile" I changed it to ".Net Framework 4", and now I have a successful build.

This worked for me too. Thanks a lot. I was trying an RDF example for dotNet where in I downloaded kit from dotnetrdf.

NET4 Client Profile: Always target NET4 Client Profile for all your client desktop applications (including Windows Forms and WPF apps).

NET4 Full framework: Target NET4 Full only if the features or assemblies that your app need are not included in the Client Profile. This includes: If you are building Server apps, Such as:

ASP.Net apps
Server-side ASMX based web services

If you use legacy client scenarios, Such as: o Use System.Data.OracleClient.dll which is deprecated in NET4 and not included in the Client Profile.

Use legacy Windows Workflow Foundation 3.0 or 3.5 (WF3.0 , WF3.5)

If you targeting developer scenarios and need tool such as MSBuild or need access to design assemblies such as System.Design.dll

Brycebryn answered 22/5, 2011 at 19:57 Comment(2)

In my case, I had 3 projects in 1 solution. I had to set them all to .Net Framework 4.5 and then I could compile! Its annoying that the error message was misleading. – Contralto 10/6, 2014 at 12:25

In my case, this all did not help. However, creating a new project, installing the same NuGet packages and copying the code did the trick. – Polymorphism 7/12, 2018 at 15:29

I solved mine because the other project was coded with .NET 4.5 and the other one was coded 4.0

Samualsamuel answered 9/12, 2012 at 13:41 Comment(1)

I had the same issue between .NET 4.0 and .NET 4.0 Client Profile. Good call. – Service 10/9, 2013 at 13:50

The using statement refers to a namespace, not a project.

Make sure that you have the appropriately named namespace in your referenced project:

namespace PrjTest
{
     public class Foo
     {
          // etc...
     }
}

Read more about namespaces on MSDN:

Using Namespaces

Molluscoid answered 21/1, 2011 at 23:40 Comment(1)

Thanks Mark, I do have the namespace appropriately named. – Coccus 21/1, 2011 at 23:53

I encountered this issue it turned out to be.

Project B references Project A.

Project A compiled as A.dll (assembly name = A).

Project B compiled as A.dll (assembly name A).

Visual Studio 2010 wasn't catching this. Resharper was okay, but wouldn't compile. WinForms designer gave misleading error message saying likely resulting from incompatbile platform targets.

The solution, after a painful day, was to make sure assemblies don't have same name.

Astrogeology answered 3/6, 2013 at 7:5 Comment(0)

It is also possible, that the referenced projects targets .NET 4.0, while the Console App Project targets .NET 4.0 Client Library.

While it might not have been related to this particular case, I think someone else can find this information useful.

Geotaxis answered 31/1, 2012 at 23:48 Comment(0)

The compiled dll should have public Class.

Concordance answered 24/4, 2014 at 6:14 Comment(0)

I had the same issue. The target frameworks were fine for me. Still it was not working. I installed VS2010 sp1, and did a "Rebuild" on the PrjTest. Then it started working for me.

Columbus answered 30/7, 2012 at 12:40 Comment(0)

Other problem that might be causing such behavior are build configurations.

I had two projects with configurations set to be built to specific folders. Like Debug and Any CPU and in second it was Debug and x86.

What I did I went to Solution->Context menu->Properties->Configuration properties->Configuration and I set all my projects to use same configurations Debug and x86 and also checked Build tick mark.

Then projects started to build correctly and were able to see namespaces.

Nurture answered 23/10, 2013 at 14:25 Comment(0)

Changing the framework to

.NET Framework 4 Client Profile

did the job for me.

Emmerie answered 1/10, 2012 at 3:17 Comment(1)

You bring up a good point: as long as all your projects are using the same framework, it should fix the issue - whether it's the client profile or an earlier version of .Net. – Coccus 1/10, 2012 at 14:33

For COM/ActiveX references, VS 2012 will show this error right on using statement. Which is quite funny, since it's saying that may be you are missing a using statement.

To solve this: register the actual COM/ActiveX dll even if it's in the neighbor project, and add a reference through COM channel, not project channel. It will add Interop.ProjectName instead of ProjectName as a reference and this solves this strange bug.

Steamship answered 21/10, 2012 at 17:30 Comment(0)

If your project (PrjTest) does not expose any public types within the PrjTest namespace, it will cause that error.

Does the project (PrjTest) include any classes or types in the "PrjTest" namespace which are public?

Aura answered 22/1, 2011 at 0:48 Comment(1)

Thanks for the insight, I'm learning a lot about this. PrjTest includes around 50 public classes; it's a decent-sized project – Coccus 23/1, 2011 at 17:40

just changed Application's target framework to ".Net Framework 4".

And error got Disappeared.

good luck; :D

Argile answered 4/5, 2012 at 10:28 Comment(1)

How to change the applications target name please? – Spilt 8/12, 2016 at 15:34

check your Project Properties, your Reference Paths should be empty like this:

Project Properties

Regards

Outrank answered 3/12, 2012 at 22:34 Comment(1)

Adding references folder of the problematic reference dll via this screen solved my problem. I guess problem is different versions of references of first level references. – Neuroglia 21/4, 2020 at 11:8

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