This is one of the most irritating build errors a developer might see, especially while setting up an existing .NET application on a fresh machine. I have found one solution that works always. Go to "C:\WINDOWS\Microsoft.NET\Framework\v2.0.50727\Temporary ASP.NET Files" ( Modify the framework version, root directory etc according to your environment. ) Now, right-click and open up the Security tabs for this folder. Grant "Full control" to the 'users' group. (Modify will also work, thought I didn't try it out) However, it this is a security problem for your environment to grant full control to all users in Users group, another Solution could be to put the concerned assemblies lo GAC which I avoided as it was not  logical to put the assemblies into GAC in my scenario. Hope this helps.