BE 2010 r3 Agent issue: "A communications failure has occurred"

Hi everyone, new to the forums and fairly new to BackupExec as well. Taken over a system from a previous worker who had things running quite nicely, however I've hit a snag with a file server which is baffling me.

The agent seems to have stopped working on a file server. It's a VM Guest Windows 2008 r2 server, fully updated and one of several very similar machines being backed up. It has the BE RAWS agent installed with AOFO option enabled. It was working happily until earlier this week, when it started throwing the error "A communications failure has occurred" and "Final error: 0xe000846b - The resource could not be backed up because an error occurred while connecting to the Backup Exec for Windows Servers Remote Agent". There's no apparent problems with the target server itself, it's happily on the network and can be connected to in all the usual ways. Nothing has changed aside from a round of Windows Updates being installed, which happened after the issue had begun.

Checking the Selection List, the server appears as a non-Agent machine. I can see file shares but no system state info or disks etc. Testing the Resource Credentials fails for this server, but works for all of the other resources in the Selection List, which are also agent-enabled VM Guest servers and are using the same System account

I have re-installed the agent several times, both as a local install and as a remote install from the BE server. Both appear to work fine and the BE Remote Agent Utility on the target server reports that the media server is registered for it to publish information to. I can't add the target server as a Favourite Resource on a Selection List  - the process appears to go through but the server subsequently doesn't appear in the Favourites list. I've turned off AV and the DeviceLock service on the target server, no joy.

I ran debugging and it generated the following when trying to connect to the agent (full domain redacted):

UNK:      [07/26/12 10:49:37] [0000]     07/26/12 10:49:37 [BESocket]           - @@@@@@@MyCloseSocket called with sockfd = 1556(0x614) retval = 0
UNK:      [07/26/12 10:49:37] [0000]     07/26/12 10:49:37 [ndmp\ndmpcomm]      - ndmpEstablishConnectionUsingNoSpecificAdapter: Could not connect to remote address 10.120.200.5 and port 10000 Errorno : 10061
UNK:      [07/26/12 10:49:37] [0000]     07/26/12 10:49:37 [ndmp\ndmpcomm]      - ndmpConnectEx: unable to connect using NetworkOptions to scsfs01.xxxxxx.co.uk
UNK:      [07/26/12 10:49:37] [0000]     07/26/12 10:49:37 [BESocket]           - BETCPConnection::CreateConnectionFromHostAndPort: Remote Host: "scsfs01.xxxxxx.co.uk": There were no addresses returned, belonging to family: IPv6.
UNK:      [07/26/12 10:49:38] [0000]     07/26/12 10:49:38 [BESocket]           - BETCPConnection::LoopThroughListAndConnect: Could not connect to remote address "10.120.200.5" Error:10061.
UNK:      [07/26/12 10:49:38] [0000]     07/26/12 10:49:38 [BESocket]           - @@@@@@@MyCloseSocket called with sockfd = 1556(0x614) retval = 0
UNK:      [07/26/12 10:49:38] [0000]     07/26/12 10:49:38 [BESocket]           - BETCPConnection::CreateConnectionFromHostAndPort: Could not create a connection to "scsfs01.xxxxxx.co.uk" because attempts with both IPv4 and IPv6 protocols failed
UNK:      [07/26/12 10:49:38] [0000]     07/26/12 10:49:38 [ndmp\ndmpcomm]      - ndmpConnectEx: All attempts to connect to 'scsfs01.xxxxxx.co.uk' failed
UNK:      [07/26/12 10:49:38] [0000]     07/26/12 10:49:38 [ndmp\ndmpcomm]      - ndmpConnectEx: failed to connect to 'scsfs01.xxxxxx.co.uk'
UNK:      [07/26/12 10:49:38] [0000]     07/26/12 10:49:38 [fsys\shared]        - FS_ResolveDevName: [\\scssql01.xxxxxx.co.uk\D:]

Just can't get the BE server to recognise it any more! Any thoughts? Anything else I can do to get it to pick up?

Any help much appreciated,

Pete Eldridge