I believe this problem is caused by a conflict with the Display Fusion utility (v2.1.1,
http://www.binaryfortress.com/displayfusion). When I stop this utility, MA3b1 stops with no problem, and when I restart Display Fusion, stopping MA3b1 causes the problem described above.

Gacck! I just had Windows Explorer lock up when stopping MA3b1 on this machine when Display Fusion was NOT running, and I also had the Explorer not lock up while Display Fusion WAS running. So now I don't know what the problem might be (or how to diagnose it, since nothing works once the lock-up has occurred).