Exchange 2013: Public Folder Mailbox cannot be deleted

Hello,

I currently have the problem that I cannot delete my "Public Folder Mailbox" , I always get the same error:

"Cannot open mailbox /o=Test Lab/ou=Exchange Administrative Group ... /cn=Servers/cn=MY2013Server/cn=Microsoft System Attendant"

The problem is the same in the Webinterface and Shell.

I already checked if the 5 Arbitration mailboxes exist and they and their user account in their AD exist.

The problem occurred when I tried moving the PF Mailbox to another Database and while the task was running the Informationservice was restarted, as a result the MoveRequest Failed with a Warning. After that I removed the Request and retried the Move but now I get the mentioned error message.

Anyone any idea how to get the Public Folder back in working condition?

Regards

Paul