I have an ASP.NET MVC 4 application. I used NuGet to update all of the NuGet packages that were installed when I created the application. One of the packages was Microsoft.B
I believe this problem is caused by the packages being read-only or otherwise inaccessible at the file system level.
Check out the entire packages folder prior to telling NuGet to restart Visual Studio to delete the packages.
I found that this could be permanently resolved by removing the packages from source control and instead using NuGet Package Restore.
I worked around this by deleting from the solution's packages folder all of the files that referenced the package in question. Specifically, these were: