JSON.Net throwing System.Security.VerificationException: Operation could destabilize the runtime

I have a web application which uses JSON.Net to write out an array of data from a .Net Array().

When run in the VS2010 environment, it works fine.

When run under IIS6 and .Net 3.5, it works fine.

When run under IIS7 or开发者_如何学编程 7.5 and .Net 3.5 when .Net 4.0 is installed (but the app pool and site is set to use v2 runtime), it fails with the exception 'System.Security.VerificationException: Operation could destabilize the runtime.'

I do not have access to an IIS7 (or 7.5) system without .Net 4.,0 so I cannot try that case.

Can anyone shed any light on this?