Not able to add media server in storage server's media server list.

Hi 

we have NBU appliance 5020, running at 1.4.4. It was getting utilised by three media servers of HPUX and 7.6.0.3.
All of sudden, for one media server it has started throwing error 83 (media open error).
We removed that media server from its media server list using credentials Tab in media server, now we are not able to add that media server in its list. It is reflecting error Server is shutdown, howvere everything is up.