We also have a 3583 LTO with 60 cartridges (advertised) capacity plus 12 I/O
slots and have seen this multiple times before.

If you call Tivoli or IBM hardware support, their answer is to shut
everything down and restart. On initialization the system will correct
itself, and it does.

The problem is, as you use the system it tends to "loose" slots. We have
been running our 3583 for almost a year and I can count on one hand the
times that we have been able to use all 60 slots.

Since we are reaching capacity and need all 60 slots, plus some other issues
(See results of adsm.org search results for 3583) we have opened a crit sys
ticket which has resulted in a firmware upgrade for the changer, library,
and all drives in our system in addition to a complete cartridge holder
change for each internal 6 pack cartridge holder to a slightly bigger slot
type. The new cartridge holders were developed to accept a wider range of
LTO manufacture's tapes.

We will see if this helps.
Mark B.