A Dynamics CRM organization with Update Rollup 4 is imported into a Dynamics CRM deployment that has Update Rollup 3. You then try to modify the security roles of a user and you get the following error "Insufficient Permissions" "The signed in user does not have the appropriate security permissions to view these records or perform the specific action."
The cause is due to the Dynamics CRM deployment not being on Update Rollup 4.
Install Update Rollup 4.
For more information on Update Rollup 4 see http://support.microsoft.com/kb/2556167