Access is Denied: c0070005

I was called in by a customer to look into a problem they had been experiencing for a long time. On their Active Directory Domain Controller, when the administrator user logs in it receives an "Access is Denied" dialogue box with "Win32" facility and "ID no: c0070005" as bellow in "Active Directory Users and Computers" by right-clicking on every object:


Another symptom was that the administrator user could not run Exchange Server System Manager. But a user with administrator privilege did not get any of these errors.
There are a lot of causes and resolutions mention on different forums, Microsoft official support website and blogs but finally I found one matching and resolving my problem Here!
The problem was that someone or some process had added Administrator user account to the "Guests" and "Domain Guests" group! I suspect that an application or process did this modification and not a user!