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Solving the “Could not copy temporary files to the output directory” error

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At times you get the error “Could not copy temporary files to the output directory” when compiling a VB.NET or C# project from inside Visual Studio. Here are some of the possible causes for this error message and the corresponding solution:

  • The target EXE or DLL file is running or is being used by another application (for example, you are using ILDASM to explore the IL code it contains. In this case the solution is quite simple: the system or the other application has locked the executable file, and you must close the running application to release this lock
  • Another VS project has a reference to the assembly you’re attempting to compile and the Copy Local property of the reference is set to False. In this case the VS project has a direct reference to your assembly (instead of creating a copy in that project’s directory) and therefore locks the file. In this case you can solve the problem by setting the Copy Local property to True (the default value). To do so, select the reference in the Solution Explorer window and then press F4 to access the Properties window, and set the Copy Local property to True.

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