error RG1000: Unknown build error

Question

C:\Program Files\MSBuild\Microsoft\Silverlight for Phone\v4.0\Microsoft.Silverlight.Common.targets(625,5): error RG1000: Unknown build error, 'An item with the same key has already been added.'

Done building project "FileName.csproj" -- FAILED.

Build failed.

Receive this error whenever i try building the soln.

Answer 1

We ran into the same problem yesterday. It happened after we merged two branches in our TFS, so we looked into the project file. There was twice the same image added to the project file. If you open that whit an XML editor you could look to a part like this:

<ItemGroup>
  <Resource Include="Assets\Images\icon.png">
    <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
  </Resource>
</ItemGroup>

Removing the duplicate parts solved our problem, but is indeed hard to find this kind of duplicates. Maybe there is a more user friendly option, that I didn't find yet.

Credits to this blog-post that did a great deal in solving the issue. On my search through the internet, I also found a bug-report. Maybe it is worth looking to that.

It also looks like there are many possibilities to trigger this error. See the following questions here on Stack Overflow:

• C#: An item with the same key has already been added, when compiling expression
• VS2010 "An item with the same key has already been added"
• Visual Studio Error: An item with the same key has already been added