Couldn't get channel number: Input/output error

couldnt get channel number: input/output error

i try to connect MC35i to GPRS , i login as root in linuxOS,then excute the following command in shell:
# pppd /dev/ttyS0 debug 9600 connect 'chat -v -f /home/chat1'&
# cat /var/log/message

Aug 3 16:36:04 localhost pppd[3069]: pppd 2.4.1 started by root, uid 0
Aug 3 16:36:05 localhost chat[3070]: abort on (ERROR)
Aug 3 16:36:05 localhost chat[3070]: send (AT^M)
Aug 3 16:36:05 localhost chat[3070]: timeout set to 50 seconds
Aug 3 16:36:05 localhost chat[3070]: expect (OK)
Aug 3 16:36:05 localhost chat[3070]: AT^M^M
Aug 3 16:36:05 localhost chat[3070]: OK
Aug 3 16:36:05 localhost chat[3070]: -- got it
Aug 3 16:36:05 localhost chat[3070]: send (CONNECT^M)
Aug 3 16:36:05 localhost chat[3070]: send (ATD*99***1#^M)
Aug 3 16:36:06 localhost pppd[3069]: Serial connection established.
Aug 3 16:36:06 localhost pppd[3069]: Hangup (SIGHUP)
Aug 3 16:36:06 localhost pppd[3069]: Couldn't get channel number: Input/output error
Aug 3 16:36:07 localhost pppd[3069]: Exit.

why? how to solve this problem? could someone give some tips? thanks