If the jobs just stay ?pending?, check the pending reason in () next to the job status in the Properties panel of the QubeGUI.
? If it states ?host missing jobtype: _____? then, the jobtype likely needs to be still installed on the Workers.
One can also check the logs. The source of many problems can be found in the log files for the Supervisor and Worker daemon. They can be most easily accessed from the QubeGUI under ?Administration->View Supervisor Log?? and ?Administration->View Worker Log?? (as of QubeGUI 5.5) when logged into one of those machines.