I added a new host to bacula today. That resulted in:
13-Oct 16:58 bacula-dir JobId 1026: Fatal error: File daemon at "oxygen:9102" rejected Hello command 13-Oct 16:58 bacula-dir JobId 1026: Error: Bacula bacula-dir 2.4.4 (28Dec08): 13-Oct-2009 16:58:39
After looking around on the web and coming up with nothing, I noticed the version difference. The new host happened to run version 3.x.y of bacula-fd, unlike my director that runs 2.4.y. Apparently bacula doesn't support the director being an older version than the client.