Cme asterisk outgoing calls porblem

i am currently using asterisk and asterisk-gui 2.0 with zaptel drivers. i have a cisco 2801 router with call manager express.
i have created dialpeer on cisco for asterisk and hav created trunk in asterisk
for cisco. i can call from cisco extensions to asterisk extensions vice versa. nw the problem is i cannot call from cisco using the asterisk analog port trunk. asterisk says [Jun 7 21:28:49] NOTICE[16409]: chan_sip.c:14703 handle_request_invite: Call from ‘’ to extension ‘35831371’ rejected because extension not found. while i can call from asterisk using cisco analog ports