I received the following error today while deploying the Silverlight WebPart in IIS.
Cryptographic failure while signing assembly 'MyWebpartAssemblyName.dll'. Access is denied.
Seems I had a permissions error. Did a bit of searching on Google and found this post on a blog by R. Aaron Zupancic. That did the trick.
I would have never thought that the permissions error had something to do with the C:\Documents and Settings\All Users\Application Data\Microsoft\Crypto\RSA\MachineKeys folder.