CryptographicException

I'm getting the following nested exception in our code on one machine
(it works on many others)

Exception: System.Security.Cryptography.CryptographicException
Message: An internal error occurred.

Source: mscorlib
at
System.Security.Cryptography.RSACryptoServiceProvider._GenerateKey(IntPtr
unknown1, Int32 unknown2, Int32 unknown3)
at System.Security.Cryptography.RSACryptoServiceProvider..ctor(Int32
dwKeySize, CspParameters parameters, Boolean useDefaultKeySize)
at CBCL.Publication.Licensing.Licence.CheckSignature()

I haven't had any luck trying to track down the problem. I suspect it is
something to do with permissions in Application
Data\Microsoft\Crypto\RSA\ but haven't managed to track down anything
wrong here. Does anyone have any ideas?

Thanks,
Nick