How to: Request Optional Permissions by Using the RequestOptional Flag
In the .NET Framework version 4, runtime support has been removed for enforcing the Deny, RequestMinimum, RequestOptional, and RequestRefuse permission requests. These requests should not be used in code that is based on .NET Framework 4 or later. For more information about this and other changes, see Security Changes in the .NET Framework 4. For information about how you can request these optional permissions in the .NET Framework version 3.5, see the previous version of this topic.