BackupExec on Windows 2003 box cannot access Linux box with backupexec agent

I have a windows 2003 SE server running Backup exec v 10 for remotley backing up all my servers. I have agents residing on all the servers. My linux box was setup by someone else before i joined the company.

The linux server is in a group called "my group" (original!) and all my windows servers are part of my Windows 2003 AD. I have no idea why the last guy put the linux box in its own group rather than adding to the domain. Is there any draw back to doing this or can you not do this???

Anyway my problem is this, my windows server running backup exec can see the Linux server (and its agent) but when it tries to connect to it, no joy! I have tried using the windows domain administrator username and password and a username and password with full access and root access on the linux box. No joy with either. It keeps saying "Logon Account "xxxxxx" failed to access "xxxxxx". The directory or file was not found or could not be accessed". All the information i can find seems to suggest i need to use the domain administrator username and password but since its not part of the domain it doesn't work.

Any suggestions would be greatly appreciated as i am not a Linux expert at all.

Thanks