Some cleaning tapes are good for 20 cleans, and some are good for 50 cleans, and varying amounts in between.
Is a cleaning tape present in the library?
Cleaning tapes do not last forever. All cleaning media only ever a specific cleaning count. And, obviously, one mount = one clean.
So, has the cleaning tape expired it's usage count?
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FYI - all LTO media (all types, all variants, all capacities, all families, all vendors) all have a tiny 'near field' (RFID) chip in them that the LTO tape drives query and update (N.B: this has nothing to do whatsoever with NetBackup) - and so tape drives can detect how many mounts any tape, including cleaning tapes, have ever had, and so tape drives know when a cleaning tape has expired, i.e. tape drives when a cleaning media has hit its maximum clean usage count...
...and so, when a tape drive requests a clean, and a cleaning tape gets mounted, then the tape drive checks the tape, and if it has had too many mounts/uses/cleans, then it simply dismounts the tape without loading it, and so the tape drive does not get cleaned.
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Anyway - your problem may be down to a mixed mis-configuration of cleaning regime. If your library is taking care of cleaning then you do not need to enter a cleaning interval of 120 or 140 hours. You only enter a cleaning interval into NetBackup if all of these following points are true:
1) The library cannot, or does not, or you do not want the library to, manage cleaning.
2) NetBackup cannot detect SCSI tape alerts for when tape drives request a clean.
3) You want to manually override cleaning alerts and force cleaning no matter whether the tape drive has requested a clean or not.
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Interval based cleaning is usually not a good idea, nor (in most cases) recommended. Most tape drive vendors do not recommend interval based cleaning - and instead recommend alert based cleaning - because the cleaning tape is a form of mild abbrassive - and each act/event of cleaning has to attempt to scratch dirt (oxide accumulation) off of the tape drive head, but not so roughly that it scratches the tape head itself. In short, too many, too regular, cleans... shortens the life span of tape drive read/write heads - and thus slowly increases the chances of read and write failures.
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If you don't know the answers, or don't understand any of the above, or you are unable to describe to yourself what your cleaning regime is, and more importantly if you do not understand why your cleaning regime is configured the way it is - then you need to start from the beginning, and read the manuals and release notes for the tape library and for the drives and read the relevant sections of the NetBAckup admin guides - and have a plan - before making any other changes.
