ASPI and SCSI Errors
Q- Do the Windows event logs (system & application) show any ASPI or SCSI errors? Does your server have any configuration conflicts with the devices that are installed? You may need to trouble shoot the server system using a SCSI Analyzer.
Q- Does the InveStore log show SCSI Request sense key information?
These kinds of errors typically deal with a communication or in some cases an electrical fault on the SCSI Bus. This interrupts reliable communication between the Host and the library device.