Asterisk Call getting Disconnected

Dear All,

I have got a problem with asterisk in PRI lines.I have set up a IVR customers will call and hear the IVR and its working fine also.The all channels will be busy always as it is an open IVR to the customers .The issue is that some times the call is not connecting to the IVR even though asterisk is running.
when i issue the asterisk -r commend in the console its showing only “Remote unix connection closed” but when i stop asterisk and start again it will again work fine.

As its a live system to the customers the IVR cant be down for a single minute .Can anybody suggest a solution.