pppd on linux

Hi i have a motorola SM modem
i have a driver for it that requires kernel 2.4.x
so i rebuilt my 2.2 kernel on RedHat7.0 and installed the driver successfully
now when i try to connect to my ISP i dial normally but when the connection is established i get ‘pppd died’ and i’m disconnected
i tried redhat dialer and kppp and i get the same error
any help?
thanx