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.
go inside properties/PublishProfiles, open the .pubxml file and check to see if your connection strings have been repeated. I had this issue, removed all the duplicate connection strings to leave one remaining and it solved my issue.