If you:

1) Register a job with quartz
2) Create an entry in the tool under jobs through the UI
3) (optionaly) create triggers
then
4) Delete the registration assosiated with the jon in components xml

Quartz throws a series of NPE's whenever the Queue is activated:

INFO: init() (2007-03-16 11:58:26,402 main_org.sakaiproject.user.impl.UserAuthnComponent)
48.171: [GC [PSYoungGen: 302252K->43643K(302336K)] 302252K->47163K(1001408K), 0.0819420 secs]
ERROR: Job DEFAULT.CTQueue threw an unhandled Exception: (2007-03-16 11:58:26,514 QuartzScheduler_Worker-1_org.quartz.core.JobRunShell)
java.lang.NullPointerException
at org.sakaiproject.component.app.scheduler.jobs.SpringJobBeanWrapper.execute(SpringJobBeanWrapper.java:72)
at org.quartz.core.JobRunShell.run(JobRunShell.java:203)
at org.quartz.simpl.SimpleThreadPool$WorkerThread.run(SimpleThreadPool.java:520)
ERROR: Job DEFAULT.CTQueue threw an unhandled Exception: (2007-03-16 11:58:26,514 QuartzScheduler_Worker-0_org.quartz.core.JobRunShell)
java.lang.NullPointerException
at org.sakaiproject.component.app.scheduler.jobs.SpringJobBeanWrapper.execute(SpringJobBeanWrapper.java:72)
at org.quartz.core.JobRunShell.run(JobRunShell.java:203)
at org.quartz.simpl.SimpleThreadPool$WorkerThread.run(SimpleThreadPool.java:520)
ERROR: Job (DEFAULT.CTQueue threw an exception. (2007-03-16 11:58:26,517 QuartzScheduler_Worker-0_org.quartz.core.ErrorLogger)
org.quartz.SchedulerException: Job threw an unhandled exception. [See nested exception: java.lang.NullPointerException]
at org.quartz.core.JobRunShell.run(JobRunShell.java:214)
at org.quartz.simpl.SimpleThreadPool$WorkerThread.run(SimpleThreadPool.java:520)

• Nested Exception (Underlying Cause) ---------------
  java.lang.NullPointerException
  at org.sakaiproject.component.app.scheduler.jobs.SpringJobBeanWrapper.execute(SpringJobBeanWrapper.java:72)
  at org.quartz.core.JobRunShell.run(JobRunShell.java:203)
  at org.quartz.simpl.SimpleThreadPool$WorkerThread.run(SimpleThreadPool.java:520)
  ERROR: Job (DEFAULT.CTQueue threw an exception. (2007-03-16 11:58:26,517 QuartzScheduler_Worker-1_org.quartz.core.ErrorLogger)
  org.quartz.SchedulerException: Job threw an unhandled exception. [See nested exception: java.lang.NullPointerException]
  at org.quartz.core.JobRunShell.run(JobRunShell.java:214)
  at org.quartz.simpl.SimpleThreadPool$WorkerThread.run(SimpleThreadPool.java:520)

• Nested Exception (Underlying Cause) ---------------
  java.lang.NullPointerException
  at org.sakaiproject.component.app.scheduler.jobs.SpringJobBeanWrapper.execute(SpringJobBeanWrapper.java:72)
  at org.quartz.core.JobRunShell.run(JobRunShell.java:203)
  at org.quartz.simpl.SimpleThreadPool$WorkerThread.run(SimpleThreadPool.java:520)
  2007/03/16 11:58:26 org.apache.catalina.startup.HostConfig deployWAR

Solution: if the registration of the job is null the schduler should handle this elegantly with warns ect and possibly flag the jobs appropriatly so they are not called