You may want to take a look at your TheSchwartz tables (some info here) to make sure that they're set up properly. The XPostWorker reads from those tables, so if the configuration for those isn't correct, then the worker won't ever get any jobs.

(Actually, if you're getting an error in the UI immediately, rather than as an inbox notification, then you're certainly having something go wrong before the XPostWorker would come into play...)