DotNet, The function call was ambiguous, no matching method was found.

Hi,

I'm making use of DotNet within NAV, I have touched on it before but having issues as below. The DotNet library in use is System.Security.Cryptography.DSASignatureFormatter.'mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089'

Many thanks, if there are any general pointers or articles that would be great.