after installing the critical patches for .NET framework, as described in the MS Security Bulletin MS11-100, some of our MOSS 2007 applications were hitting the following exception:
FileLoadException : Loading this assembly would produce a different grant set from other instances. (Exception from HRESULT: 0x80131401
It seems that the security fix applied in the patch KB2657424 (maybe also KB2656351, although it’s a different version of .NET framework) has caused this temporary problem. The solution is to recycle the affected applications’ IIS pool – the exceptions don’t occur anymore and applications work correctly again.
The solution with restarting application pools appears to be quite strange, since the whole machine had to be restarted upon installation of those security updates. But still, it worked.
Hope this helps,