You do not have sufficient permissions. This operation can only be performed by a manager of the group

Issue/Error: You do not have sufficient permissions. This operation can only be performed by a manager of the group." error message when you try to change the "ManagedBy" attribute in an Exchange Server 2010 SP1 environment

Resolution: Install Update rollup 3 for SP1.

Reference: http://support.microsoft.com/kb/2487852