Hello,
As your problem seems to be with slow Backups please refer to the following technotes and let us know if they are useful.
(title) What Backup Exec settings can be modified to reduce the amount of time it takes for a backup to run?
http://support.veritas.com/docs/249090
(title) How to correct slow backup performance, slow virus or pre-job scans, and agent initialization problems on fragmented Windows NT, Windows 2000, and Windows 2003 server partitions
http://support.veritas.com/docs/237444
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