Could not load file or assembly 'EntityFramework' or one of its dependencies - Strong Name verification

I've recently started to get the following error in my .NET 4.5 MVC-Application:

Could not load file or assembly 'EntityFramework' or one of its dependencies. Strong name signature could not be verified. The assembly may have been tampered with, or it was delay signed but not fully signed with the correct private key. (Exception from HRESULT: 0x80131045)

How can this happen? I already checked the validity of the EntityFramework.dll (using sn.exe -v) and also re-downloaded it using the NuGet Packet manager... But still to no avail.

How can I overcome this?