Modem will not disconnect

[Slammy1]

My friend has an older Dell system (GXa PII-300) and had some problems on installing a USR 56k Fax modem in Win98. The modem does not seem to hang up on disconnection. The network closes OK, and there does not seem to be any connection present, but to hang up the phone you have to physically remove the jack from the wall and plug it back in. It may be related to a registry error that came up during dialer installation. ccRegVrfy finds a problem but cannot autocorrect, neither can Norton System Works. Those seem the only problems. Any ideas? I've tried reinstalling the modem a few times, reinstalling the dialer, but the problem persists. TIA for any help.