This message appears in the SCSI log to indicate that a read or write operation has been retried until it timed out. With SCSI disk the time-out period is usually 30 seconds; with tape, the period is usually 20 attempts. Time-out periods are generally coded into the drivers.
Check that all SCSI devices are connected and powered on. Make sure that SCSI target numbers are correct and not in conflict. Verify that all cables are no longer than a total of six meters, and that all SCSI connections are properly terminated.