I was scratching my head for 10 minutes while attempting to breadboard a circuit on a Board of Education without a BS2 yesterday. Mainly testing the onboard FTDI adapter, those LEDs were flashing but my circuit was not working with a 9V battery attached. I checked for +5V (Vdd) at the BS2 socket (where I was connected) and only got ~0.75V... Did I burn out the regulator? No, 5V everywhere else on the BoE. Burn a trace? Couldn't find anything... Finally realized that the BS2 socket is only wired to Vin, not Vdd, and the Stamp uses its own 5V regulator. Doh!
Still making mistakes late in life. Being 39 sucks!