After you compile your Web application, you may receive the following error messages in the Microsoft Visual Studio .NET task list:
Could not copy temporary files to the output directory.
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The file 'bin\mywebapp.dll' cannot be copied to the run directory. The process cannot access the file because it is being used by another process.
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The file 'bin\mywebapp.pdb' cannot be copied to the run directory. The process cannot access the file because it is being used by another process.
Additionally, the ASP.NET worker process (Aspnet_wp.exe) may hold a lock to dynamic-link libraries (DLLs) in the Bin directory.