1: Sub PlanWizardDatabase.Destructor()
2: Sub PlanWizardThread.Event_Run()
3: Sub APThread.Event_Run()

User description of above error trace:

I tried to remove the duplicates in a plan created with the PlanWizard (PlanWizardThread still hasen't finished)

Fixed. If you attempt to use the PCW while the background thread is busy, you'll be asked to come back later.