Exchange Mailbox Error: "Active Directory operation failed on *DC*. This error is not retriable. Additional information: Insufficient access rights to perform the operation."

While deleting a user migrated from Exchange 2003 to 2010 you can face the following error. The issue can be very irritating with a very simple  resolution.

Resolution:

1. Open ADUC
2. Click View-> Select Advanced Features
3. Find the user in Active Directory
4. Right Click User-> Properties -> Select "Security" tab
5. Click on Advanced -> Check “Include inheritable permissions from this object’s parent” and then click [OK] twice.

This should resolve the issue for you, if not the Happy Troubleshooting :)