Question: 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?

Answer: 
I had the same experience but due to duplicate image resources in the .csproj file:

```
<Resource Include="Images\trigger-ModuleSelector1.png" />
<Resource Include="Images\trigger-ModuleSelector2.png" />
<Resource Include="Images\document.png" />
<Resource Include="Images\folder.png" />
<Resource Include="Images\trigger-ModuleSelector1.png" />
<Resource Include="Images\trigger-ModuleSelector2.png" />

```

Probably from a Merge Gone Wild(tm).

Same symptoms--regular build OK, rebuild fails.
Remove the duplicate resource entries to fix the problem.
I just had this same problem, but I didn't have any "Resources.resx" file in my solution (I didn't have any \*.resx files, for that matter). My problem came because my .vcxproj project file was trying to use a file twice. I had added a custom build step for my protobuf files and added all my \*.proto files to my project. However, a rouge .proto file appeared twice. Getting rid of the duplicate solved the problem.

So if you're having the same problem and you don't have any Resources.resx file, try looking at your .vcxproj file and making sure there aren't any other files that are getting duplicated.