Remote Access Connection Problem

[Kim Willsher]

I'm running an iMac on OS 9 (yes I know it's out of date but my broadband modem won't work with OS X) with an external Alcatel Speed Touch USB modem.
I connect but after a time - from 10 mins to 1 hour - the remote disconnects. When I try to reconnect I get the message "The remote side is not responding correctly. Check the configuration of your control panels and try again".
Configuration has been checked and is fine. ISP tell me line has been checked and modem are both fine but I still cannot connect. Each time I get the "remote side not responding" message. However, bizarrely, if I restart the computer I can connect, but again it disconnects after a time and again I have to restart.
I've zapped the PRAM and cleared IE and Netscape caches/history. I tried dumping the Outlook Explorer Preferences as someone somewhere suggested but that just deleted all my Hotmail messages from the system so I replaced OE Preferences.
ISP people are extremely unhelpful...the best they came up with was that my iMac was the problem and it was something to do with the computer not "synchronising" with the modem. They could not suggest what to do about this. However I have examined the remote access log record and it definitely says "termination requested by the remote side" on each occasion.
Do you have any idea what is going on?