You've got the Palm Contacts, Calendar, and Tasks conduits enabled, and you've also got the Apple iSync conduit enabled. Contacts synchronizes the address book / contacts database, while Calendar synchronizes the calendar, and Tasks the to-do list; all directly with the Palm Desktop software database. The iSync conduit synchronizes all 3 databases with Mac OS X SyncServices, which will be synchronized to iCal and Address Book, to .Mac, and any other SyncServices clients you might have enabled. You can't enable two conduits that want to sync the same database, so the HotSync complains.
So the question is: where do you
want the data to go? If you're using the Palm Desktop to view/change contacts, calendar, and to-dos on the Mac, then you should just disable the iSync conduit. (Move it out of /Library/Application Support/Palm HotSync/Conduits) But if you're using iCal and Address Book, or the Chronos SOHO Office PIMs (which are also SyncServices clients), then you should disable the Palm conduits instead.
Even better, since a Palm TX has the new Palm databases, consider buying The Missing Sync to replace the Palm HotSync mechanism entirely. It's more reliable and has far better support. It also comes with SyncServices conduits that are far superior to Apple's iSync conduit.
The iSync conduit was written back when the default Palm calendar didn't have category support, for example (even though many people were using datebk or Handspring's licensed datebk variant, which
did have category support). The new Palm calendar application does support categories, and if you use them you'll be extremely unhappy with iSync because it hasn't been updated in years. The Missing Sync's conduits support categories, as well as contact photos and other features of the newer Palms.