Now and then the program may just appear to balk and stop, usually with an “illegal operation” message. This is usually due to an improperly entry sequence, most often occurring during stem design.
Familiarize yourself with the sequence of entering data, and don’t switch back and forth between screens too quickly, as this can be a trigger for a lock-up. Don’t hurry it. If it does lock up, you may need to reboot. If you continue to have this problem, let us know and we’ll see if there may be something systematic that could be causing the problem.