Visual Studio Error: An item with the same key has already been added

Question

When I'm trying to change the default Image of a Control on Windows Forms in Form Designer (no matter where on which control) I get this error:

Error message: An item with the same key has already been added

I tried to delete and recreate the Resources.resx file.. I assured that only 1 resx file with these keys exist.. (in fact that's my only resource file) but it still does not work.

I have som strings in it and some images. That's all.

Any idea?

Holub

maybe there are more than one item in aspx with same ID. – Yarak

Sorry I forgot to mention I'm using WinForms – Holub

I'm getting this too completely out of the blue - even though the official build (which I have re-gotten from TFS) is fine. Something is wrong somewhere in the system and I can't find which temp file to delete. Even tried rebooting. – Selfcontradiction

Actually I'm getting it as part of the build, in an ASP.NET MVC app so Kirill's answer doesn't help. – Selfcontradiction

Answer 1

I had this problem too. The solution is to never create a .resx file with the name "Resources.resx" because it conflicts with the "Resources.resx" files that can be automatically created in the project's properties dialog.

Just right-click and rename the "Resources.resx" and you should be able to change images perfectly.

Cazares

I'm getting this problem, but I don't have any .resx files. What else could be the problem? – Nowhere

The bug is still present in VS2012. :-[ – Penance

Still present in VS2015 (update 3)! But, I am working on C++ (library) and now how am I supposed to know what is causing this error?! It is literally, the only error that stops the project from being built.. Any ideas? – Bordie

Answer 2

If you really want to figure out what is going wrong, you can try and attach a debugger to VS and break while devenv.exe is showing the message box. From the call stack it should be obvious what VS is doing. Here are more details about debugging Visual Studio: http://blogs.msdn.com/kirillosenkov/archive/2008/12/07/how-to-debug-crashes-and-hangs.aspx

If you like, you can post the call stack of the Visual Studio main thread here and I can try to investigate what is going on.

Handoff

Answer 3

Was getting this error while adding a project to a solution. None of the above metioned scenarios applied but restarting visual studio fixed this. Silly, yes. Visual studio version - 2015 enterprise.

Sinfonietta

Yep, that fixed it for me on Visual Studio 2019. Typical Microsoft, restart fixes things :/ – Roncesvalles

Answer 4

I had the same issue. But in my case it was because I had twice the same file listed in my resources folder. Probably a problem after a merge.

Steeplejack