Excessive Line Voltage

I receive an error message “excessive line voltage disconnect phone line from modem or damage may occur” when the line isn’t even plugged in(checking to see if it detects a dialtone. It responds in the control panel). Other units on the same line don’t have that problem. I’ve never seen this problem before. It’s an Emachine 333k with an Eiger Labs modem(chipset PCT789T-A). I’ve tried 8 different drivers with no luck. The problem occured after a fresh standalone reload of WIN98 1st edition. Any thoughts or ideas would be appreciated.