Backupexec 8.6 and Exchange 2003

Using 8.6 and ab;e to backup exchange 2000 but now tyring to backup ex2003 server and I get the error:

Unable to attach to \\GB-ESH-EXC-2\Microsoft Information Store\First Storage Group.
The item was not found.
^ ^ ^ ^ ^
Unable to attach to \\GB-ESH-EXC-2\Microsoft Information Store\First Storage Group.
^ ^ ^ ^ ^

I've checked the KB and the ex agent I have installed should be capable of backing up ex2000 and ex2003.

I've installed the Ex2003 System Manager onto the backup server and that doesn't make a difference.

Any help would be really appreciated.