A value of 255 in the wrong place will not cause a Basic Run error, unless you're very lucky. Instead, it'll make your robot do a "not-so-happy" dance, with random LEDs blinking and whatnot, due to the problem Jim mentioned, that the SEROUT command gets screwed up. We had this problem in 2002, and it took a bit of time to figure it out
.
Instead, one thing that I've noticed, unless you have any debug statements, leaving the serial cable in the Programming Port will trigger an error, I believe a Basic Run error, but I can't remember what exactly.
Another possible problem is that someone touched the uP init section, and I'm pretty sure that can't be touched or it'll break. Also, make sure you use the Constants section correctly, because I believe any value used in SERIN and/or SEROUT must be "signed" by a Constant. It's been a while, so I can't remember exactly, but definitely check the default code on
www.innovationfirst.com/firstrobotics to make sure nothing crucial changed.