Welcome to the world of Tivoli Storage Manager, Dave...

Client option PASSWORDAccess Generate may be in effect on your
Macintosh systems, resulting in some confusion.  (That is the
resulting default when you install the Mac client scheduler by using
the setup assistant.)  With that option in effect, client password is
saved in a special place (/Library/Preferences/Tivoli Storage
Manager/) when the administrator issues the first client-server
operation and is prompted for the client node password, which is then
stored on the client as a result of the option.  Where the node
password gets changed, this interactive password deposition has to be
done again by the administrator, to get back in sync with the
password as known by the TSM server.

You say you are using cron for backups.  There were various problems/
issues with the scheduler in earlier 5.x levels of the client,
reportedly resolved in more recent levels.

Beware the gotcha of the MEMORYEFficientbackup option default being
Yes in the Mac client, which debilitates performance.

   Richard Sims    http://people.bu.edu/rbs/