The initial debugging question has to be asked first in this problem:
had these backups been running successfully, and then one day they
stopped working? If so, then the site changes journal needs to be
consulted to see what site configuration changes were made.

An example is seen in the List archives, where one customer had changed
a storage pool targeted by a management class, but forgot to activate
the changed policy set.
Changes in the site firewall may also be at play. Or perhaps site
networking realignments, such that the TSM server can no longer reach
the clients per the address it last had for them. Or the client options
changed their port number. (If suspect, you might try defining the
HLAddress and LLAddress for one problem node.)

Also, consider boosting your 5.2.2.0 server level, as problems like
IC37862 may be fixed in a higher maintenance level.

   Richard Sims