Recovery for Exchange: Active Directory Error

Everytime i try to do a Backup, i get the following Error in the log:

"Active Directory Error: -2.147.463.168.; Last Error (0): "; Provider: 'LDAP Provider'. (translated from german)

The complete Backup Task stops and no Backup is done. I tried several things, like giving the User the rights mentioned in the knowledge base and granting all rights to the information store with add-ADPermission etc.

Same Error appears, when i try to backup single Mailboxes.

Any hints or suggestions? Thx!