Miles: Cleaned up some of the code for CustomerIDsFromReservationsForFranchise(int) and AllCustomersInFranchise(int); everything seems to be working now. Tracked the problem down through additional functions, and found that it finally crashed in "public void setList" on line 42 of CustomersOverviewPanel . The ArrayList makes it all the way there with its contents, but for some reason the CustomersOverviewPanel doesn't like it.