Today I ran into an issue that I had not encountered (at least not in this manifestation) while compiling an assembly so I thought I'd share the solution.  The error was simply:

Cryptographic failure while signing assembly '....' Access is denied.

As it turns out I had just rebuilt my laptop from the ground up.  I don't run my computer in an administrator capacity and my process of installing was, this time, a little different that how I usually rebuild my machines; I made sure I wasn't an administrator immediately upon having installed Windows.  However, rather than temporarily promoting myself to Admin via the MakeMeAdmin utilities to install my development environment, I installed VS.NET while logged in as the Administrator user directly.  The byproduct of this was that my non-administrator user account was never granted permissions to a required directory for signing assemblies.

To remedy the problem I simply opened an Explorer window as an administrator and altered the ACLs on the necessary directory.  I granted my user Full Control on %ALLUSERSPROFILE%\Application Data\Microsoft\Crypto\RSA\MachineKeys.  Simply restart Visual Studio (if it was open) and you should be off and rolling.