Serial data corrupt on ONE computer....

...would have worked just fine.

I have no way of knowing why you didn't use the volatile keyword. Perhaps you were aware of it, and had good reasons for not using it. I offered you a change to explain them. If you weren't aware of the volatile keyword, you could google it, or ask here, and we could offer (more) advice.

I don't think I was being condescending. At least, that wasn't my intent.