Hi Geoff (and all folks ...)
I just wanted to add a little thing to what my enlightened predecesors said : 
the 3575 library is a kind of very sensitive animal : it doesn't like to be 
manipulated manually, that means if any technician has oppened the door and 
pushed the eject button of your drives to get the "stucked" tapes back, it 
didn't appreciate it at all, that's the reason why you had to stop your system.
This library has a kind of internal inventory : if something is done by hand, 
the machine doesn't keep track of it, and when it realises somethin doesn't 
match with what it considers as beeing it's content, it simply hangs !
Rebooting the systems just obliges the library to re-do it's inventory ...
But be aware of the fact that TSM is not informed of those modifications until 
you perform an audit of the library, or you restart the program.