The CAS security policy revolves around two key concepts - code groups and permissions. Each .NET assembly is a member of a particular code group, and each code group is granted the permissions specified in a named permission set.
See CAS objects -- Run 'caspol -lg' from command line.
Add CAS objects -- caspol -ag 1.3 -site www.mydomain.com FullTrust
Change CAS obj -- caspol -cg 1.3 FullTrust
Turn Off -- caspol -s off