Exchange 5.5 backup probs using Arcserve Brightstor 11.1 (build3200)

When trying to back up the information store on the exchange box’s the through put drops from 250mb to 100/70kb a minute! Brightstor all patched up & reinstalled. Exchange is running on NT4 (SP6) & WIN2K (SP4)& backing up to a WIN2003 box.