Thanks to everyone for your replies.

We have now found the solution.  We done a firmware upgrade of the ADIC library 
and the individual drives, this thankfully has solved the problem.

+----------------------------------------------------------------------
|This was sent by lesley.mccormack AT east-ayrshire.gov DOT uk via Backup 
Central.
|Forward SPAM to abuse AT backupcentral DOT com.
+----------------------------------------------------------------------

To sign off this list, send email to listserv AT listserv.temple DOT edu and 
type "signoff networker" in the body of the email. Please write to 
networker-request AT listserv.temple DOT edu if you have any problems with this 
list. You can access the archives at 
http://listserv.temple.edu/archives/networker.html or
via RSS at http://listserv.temple.edu/cgi-bin/wa?RSS&L=NETWORKER