You can no longer add partial trust Solution Packages to the bin directory. Any files deployed to the bin directory must be full trust. Any deployment scripts needs to be updated to make sure that they specify the correct trust level. After the release of .NET Framework 4.0, the GAC was split into two, one for each CLR.

c:windowsassembly is the location for .NET versions 1.0 through 3.5 and c:windowsmicrosoft.netassembly is location for all the dlls for project Created in .NET Framework 4.0.