cp210x.ko hangs on open attempt

[Roger K. Wells]

I have a RS485 serial device (Quatech SSU2-300) that when plugged
into a USB (2.0) port appears to be recognized correctly. dmesg yields:

cp210x 3-1:1.0: cp210x converter detected
usb 3-1: reset full speed USB device using uhci_hcd and address 8
usb 3-1: cp210x converter now attached to ttyUSB0

A "C" language program attempting to use this port hangs at the
open call.

This same program with the same device worked on a Centos 5.5
install on the same computer.

uname -r : 2.6.34.7-56.fc13.x86_64

The USB device works in Windows XP so I don't think there is a defect
there.

Any thoughts will be appreciated.
THX