Unable to copy file reference.dll to bin/reference.dll. The process cannot access the file reference.dll because it is being used by another process

Question

For one of my ASP.NET 3.5 applications, every single time I try to build the web app, it throws the following build errors in Visual Studio 2008:

Error 16

Answer 1

I had this issue on a web project with System.Web.Extensions.dll from the Microsoft Reference Assemblies folder. Setting "Copy Local" to false in the reference properties fixed it.