New Post: NAnt extension getting Inheritance security rules violated while overriding member error

I believe this is related to a change in the security model for .NET 4.0. I have added the SecurityCritical attribute to the method in your exception and have posted a .NET 4.0 build under the issue you posted. Please check it and confirm it resolves your issue and then I'll get it added into the next release (2.3.1).