All of a sudden, whenever I try to connect to an ISP using a U.S.Robotics serial modem on linux (suing kppp), I get a stupid LCP timeout and get disconnected. The modem dials fine and connects to the server, but during the logon phase there seems to be no response from the server (the RD light on modem is never turned on) and then it terminates. The ironic thing is this problem has occured since only a few days ago, I had no problem connecting before that.

Note that I've tried quite a few ISP's (all of which worked fine beforehand), and the problem doesn't exist in Windows.

that might just be your isps authentication server is off line or full up or they acidentay deleted your account or something

No it isn't, since it's not just one ISP, and I don't have any problem connecting to them on Windows either.

Could someone please help? The last thing I'd like to do in Windows is going online.

After a lot of googling, I tried what was suggested here, and still no luck.

I'm giving this thread one more chance before I give up hope...