Any ideas what may have gone wrong? Are there any tools to run diagnostics on the tape unit?
I assume we are talking about a DAT 36-72 drive here ?
I know of some diagnostic tools that run on Linux for DLT, but I have never used anything on a DAT drive, DLT is easy as only about two companies actually build the drives (quantum and tandberg). But I think with DAT you may be needing device specific tools.
Some drives are very fussy about block sizes, check your drive specifications and use the mt command to set this up. Although why only now this has would become a problem I am not sure.
Sometimes I have heard that the mt command can report useful information when asked to show drive status, you may see a count of read/write errors etc.
If we are talking something like DAT or AIT then is the tape rewound enough to fit some data on ? Sorry a bit of a newbie question, but I thought I'd check.
I have seen grey beard Unix admins use the cpio command in mind bending ways to test tape devices before, but please don't ask me to recite any of it :-)
Also remember that the cleaning light is only a guide, Although it's not good for the drive to run a cleaning tape through it too often, in this case it may be worth a try.
Dud tape ?