Outbound call from xlite showing error

I m trying to make call out using Xlite with user id 7591618 to any mobile number it is showing this error,
NOTICE[2567]: chan_sip.c:20792 handle_request_invite: Call from ‘7591618’ to extension ‘9856654776’ rejected because extension not found in context ‘Expert’.

While i am with some other id which is in sip_buddy table the call goes through and it works.

the extensions i have written for expert is
exten => _X.,1,Dial(DAHDI/g1/${EXTEN})

which is only working few user ids and other ids…
please do the needful
Anshul POrwal

E versus e?