[AD] Error ID no 80072030 "There is no such object on the server"

For managing the Active Directory I use an account that is a Administrator & Domain User.
This has worked for years, never a problem. But lately, when I try to modify an existing User/Group I get the error:

There is no such object on the server

Facility: LDAP Provider
ID no: 80072030
Microsoft Active Directory - Exchange Extension

When I use a different account (same specs) there is no problem...
Can anybody tell me what this error is?
What can I do about it?

With regards,
Goldhorn.