Those are some good points, and I'm looking into them. I should have specified that when I said I moved it around, I did not mean in the system itself, but outside (I had to relocate systems so they could be plugged into a UPS). So I can be sure it isn't an IRQ problem.

I am looking into all the other possible hardware problems, but, in the meanwhile, it would help a LOT if I could rule out software and config problems. (It's really hard pursuing this problem on 2 fronts and I'm hoping to narrow it down.) If I could be sure that the function I mentioned will always work, it would help -- or if I knew that the method I'm using in calling the function in Device::SerialPort was unreliable, it would help me a LOT in my troubleshooting.

In the meanwhile, I'm still working on the hardware issue. I'd just like to see if I can rule out the software/config end or find out if there are things I can check there. Thanks.