VS2010 "An item with the same key has already been added"

I recently installed Visual Studio 2010 and copied and converted an old VS2005 solution to VS2010

When I edit this solution, if I try to change a control's .image property, VS2010 creates a message box telling me that "An item with the same key has already been added", and won't let me browse for an image.

I can add images for any other solution, even others ported from VS2005, but not this one. Any idea what I'm doing wrong?

I worked this out thanks to a search. 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.

Once I renamed Resources.resx to Icons.resx, I was able to change the image property for anything in the solution.