Backup Error

The following error is received periodically when performing nightly backups:

Verify of “E: DataStore”
Backup set #3 on storage media #1
Backup set description: “DocLink System”
Verify started on 10/11/2006 at 3:19:48 AM.

Storage device “DELL 2” reported an error on a request to read data from media.

Error reported:
The semaphore timeout period has expired.
^ ^ ^ ^ ^

A few years back, an Administrator told me that was due to a dirty drive. The drive is cleaned on a weekly basis.

This is on a Dell Poweredge 4600, W2K sp4. The program is Backup Exec.