"Cannot create temporary redo log directory" when performing VCB operation with BackupExec

I'm using VCB with BackupExec but when I run the pre-backup job, it fails.

The logs it produces contains the following

Could not update cache.

Error: Error while opening disk vpxa-nfc://[47cffc9b-20495446-13de-001e4f25621d] Live_VCoyote/Live_VCoyote.vmdk@esx2.zoo.lan:902!52 f8 d5 a8 95 c7 d7 b8-63 a4 33 86 76 9e 56 43: A virtual disk could not be opened. -- Cannot open disk file: Error : Cannot create temporary redo log directory.

Unable to check for the existence of an old redo log or failure to choose a filename for a new redo log for disk 'vpxa-nfc://[47cffc9b-20495446-13de-001e4f25621d] Live_VCoyote/Live_VCoyote.vmdk@esx2.zoo.lan:902!52 f8 d5 a8 95 c7 d7 b8-63 a4 33 86 76 9e 56 43'.

Failed to configure disk scsi0:0.

An error occurred, cleaning up...

We're running VI with ESX 3.5 Servers having SAS drives i.e. no SANs here

When I run "vcbMounter.exe -h <server> -u root -p <pw> -a name:<name> -r e:\vcb -t fullvm -m nbd" it all works fine so before delving into the BackupExec scripts thought I'd see if anyone knows what a "temporary redo log directory" is or has had a similar problem

Thanks in advance for any replies

Phil