Upgrade 1.1 to 1.3 causes ReflectionTypeLoadException on bootstrap

Jan 6 at 12:40 PM
I've just been given time to update the libraries used in our product. I'm moving from version 1.1 to 1.3 but when I try to just perform a straight upgrade via Nuget I get the following exception.

An unhandled exception of type 'System.Reflection.ReflectionTypeLoadException' occurred in mscorlib.dll

Additional information: Unable to load one or more of the requested types. Retrieve the LoaderExceptions property for more information.

Can anyone suggest what might have changed between these releases to cause this or how I can get the LoaderExceptions?