MSBUILD : error PFE004: Assembly could not be found: 'Sdl.Core.PluginFramework'

The following error occur when project build on Visual Studio.  

MSBUILD : error PFE004: Assembly could not be found: 'Sdl.Core.PluginFramework'

What is the cause?

 

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I make new Trados addon project watching a sample project.

The sample project success to build.

 

I add a following line to my new project file.

<Import Project="$(MSBuildExtensionsPath)\SDL\SDLTradosStudio\14\Sdl.Core.PluginFramework.Build.targets" />

Then occur above error.

If remove this line, success building.

 

There is "Sdl.Core.PluginFramework.dll" in the bin/debug folder after building.

 

The file "Sdl.Core.PluginFramework.Build.targets" is not change.

 

in Sdl.Core.PluginFramework.Build.targets:

      AssemblyFilePath="$(TargetPath)" 

 

(I think $(TargetPath) = bin/debug.)