PEBCAK: Problem Exists Between Chair and Keyboard.
Check. Spent way too long trying to figure out why a machine would not communicate with an UPS, no matter what the settings. Varied everything. Checked the BIOS. Tried a different driver. RTFM. RTF-FAQs. Searched the mailing list archives. Googled everything I could think of. Finally pulled the cable and tried the tests again. Same result. Doh. Serial ports blown. Darn hardware.