Hey I just learned that lesson the hard way! I sent a test prog to my pal in TX and the damned thing wouldn't run on his crappy old imac....mainly because I forced the refresh rate to somn specific. I took out that part and voila! It worked!
Out of curiosity, did you set it to something high, or low?
I'm using an LCD monitor myself, which tend to be a lot more forgiving to 'weird' refreshrates than CRT's are.