I have an HP MSL 5026 on my SAN. The backup server is running ArcServe 11.5. I upgraded from 11.5 to 11.1 a few weeks ago. This past thursday many of my slots were coming up as unreadable. When I do an inventory I get mixed results either it displays the media correctly or it show the slot as completely empty. I have put new tapes into the library and still we are getting the problem. I ran HP's diagnostic on the drives and it came up with one or more critical errors on one of the tape drives (it has 2 SDL320 drives) The technician came out yesterday and replaced that tape - even though when he got here we couldn't reporduce the critical errors message. After replacing drive 2 I was still getting the unreadable media problem. So to make sure it wasnt a problem with the first drive I put the first drive offline thru Arcserve and did another inventory. Only the new drive reading the media but same problem. After doing repeated inventories I got all the slots to show up as empty or blank media last night. When I came in this morning its telling me to insert blank media to complete the job!! I checked and several of the slots are showing up as unreadable in that job group. I'm new to ArcServe and the MSL SAN library. I inserted a tape through the mail slot hoping it would go ahead and write to that tape but I don't see any activity on the job. What are the next steps I should take to diagnose this problem?