Is this a2billing bug

I have create a cardnumber by a2biling and i can loggin with the cardnum,but when I call any number ,the message is 404 not found.
From log output, it seems a2billing bug,because their no context callingcard definded in extension.conf. I dont know whether i am wrong.
Anybody met the same problem?Thanks

an 5 15:12:32 DEBUG[4263] chan_sip.c: Setting NAT on RTP to 524288
Jan 5 15:12:32 DEBUG[4263] chan_sip.c: Checking SIP call limits for device 4938629918
Jan 5 15:12:32 NOTICE[4263] pbx.c: Cannot find extension context ‘callingcard’

Anybody have met the same problem?Thanks

aren’t you better off asking either the creators of a2billing, or over on the A@H forums where just about everyone there at least has the software to hand ?