When compiling I get "Could not copy temporary files to the output directory" or "The process cannot access the file because it is being used by another process" error messages. Why?
Visual Studio .NET is unable to copy your DLLs from Bin directory to a temporary ASP.NET files folder. This is due to having a trailing backslash in root web application, or in a virtual directory with child directories marked as Web applications.
For more information refer KB Q319991