ArcServeIt Backup Error

I have a Novell Netware 5 Server using CA ArcServeIt 6.6 & an HP SureStore 5000 drive. I recieve the following error 3-4 times per week, failed to open directory error=0, Netware error=a8. I have 2 volumes, they are sys: and data:. It only happens to the data; volume.