I would like to add, I had to do the serial numbering for XP usage.
W7 "virtualizes" ports just fine even if all devices have the same serial device numbers.

I also needed to remove all hubs and miners from machine to run the utility without errors, on XP.
Insert One USB Miner on XPmachine at a time and run utility.

ANT U1 & U2 also.

This seems to be a XP only issue.