I know Erik will hate me for this, but I tried loading BAS52_B3.HEX (fixed 9600 baud version) in Pinnacle Simulator and it seems to work fine. I was able to do the FOR I=1 TO 10:PRINT I:NEXT I instruction just fine. I was also able to add the line 100 PRINT "A" just fine, list it, and run it.

The ERROR:C-STACK means a "stack overflow" according to the soruce code.

I tried logging on to your device and tried manually "poking" in the data for my 1-line program using XBY. I tried poking in data from 200h (512) through 208h (520). What I found is that I was able to assign 512 through 515, but when I tried XBY(516)=34 I always get 11 back when I PRINT XBY(516). It's like I can't modify that address. Nor can I modify 517, 518, 519, or 520.

I'd say that's probably your problem. What's causing it, though, is something I can't say.

Regards,
Craig Steiner