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.

Answer 2

You could download the excellent SysInternals Handle program. This will tell you which processes have a lock on the files concerned.

If it is an external program (e.g. virus scanner/indexer) then this should help. If it just reports Visual Studio (devenv.exe) as the culprit, then it will be of less help!

Answer 3

Check if the user dll and the application referencing the dll target the same .NET framework. I had a case where the frameworks were different which caused this problem.

Answer 4

Just go to \Debug\bin and delete all .dll files.

Working great for me.

Answer 5

Delete the binaries from the bin\Debug folder and recompile them. This works for me!!!

Answer 6

I didn't have any luck with the pre-build events unfortunately. What worked, in typical IT Crowd fashion, was to quit Visual Studio and reopen it.