I am using the Tripp Lite USB to serial adapter. I have verified the adapter is installed properly and the adapter shows up on Com 4 on my PC under Ports (Com & LPT). The port setting is port 4 in HHST. I have all baud rates set correctly and I still get an error in serial communications after several seconds.
If you have a wireless device enabled on your PC or laptop this can interrupt the serial communication. Go to Network connections and verify your Wireless Network connection type LAN or high speed internet is disabled. Even it says disconnected you should disabled it. This has been known to help in cases where everything is set up properly. Wireless devices such as Palm Pilots can cause this also so disable all wireless devices that you use.