[Coco] Unusual problem

[Bill]

I have an unusual problem. I have a Coco 3 that acts very strangely. 

When hooked to my PC (running XP SP3) in the shed, it works great. 

It will read DriveWire 4 without a hitch, and it will run BOTH RS-DOS and
NitrOS-9 disks beautifully. I save a NitrOS-9 image to a physical disc, and
it boots with no problem.

HOWEVER, when I bring it into the house and hook it up to my PC in the
office (also running XP SP3), it will not run ANY NitrOS-9 images from
DriveWire. I load a standard 40tk NitrOS-9 image into Drive 0, type DOS, and
all it does is come back with 'OK'.

Both computers have identical dual serial port cards in them with identical
drivers. They are even running on the same ports (Com6).

Ideas?

Thanks