Can't add Microsoft SBS 2003 to Acronis Management Server

Hello,

we are using ABR11.5 to Backup our servers. The Acronis Management Server runs on Microsoft Windows Server 2008 R2.
Some days ago I recognized that one our our servers (SBS 2003) reacted strange.
In the AMS it was listest as last connected some days ago, an says the last goog backup was some days ago, too.
But looking into the correspondig depot I could still see a backup for every day. So I tried to connect directly to the server from within the AMS without success. I didn't get any errors, but the message "Connecting to server..." stood there forever.
On the other hand I could log in directly to the server an start the local Managment Console without problems.

So I decided to delete the sevrer from the AMS an reconnect ist. Deleting it was no problem.
But now I-m not able to add the machine back to AMS.
No matter if I try to add it from the local Managmemt Console or from within the AMS, I will only see the message "Adding machine to server".
No errors, no logs, just this message.

Last time I waited for over 8 hours before canceling the action.

Any ideas?