Hangup on answer

I am having an issue with phone calls made using Polycom 33x phones. The FreePBX phone system can receive calls no problem, but when it tries to make calls, it will dial and then as soon as the person answers, the phone system disconnects the call and throws the following error:

[2013-10-07 08:03:03] WARNING[1749][C-00000012]: chan_sip.c:15745 __set_address_from_contact: Invalid contact uri (missing sip: or sips:), attempting to use anyway
[2013-10-07 08:03:03] WARNING[1749][C-00000012]: chan_sip.c:15758 __set_address_from_contact: Invalid URI: parse_uri failed to acquire hostport

Is there something wrong in my sip config for the phones? I have 2 Cisco ATAs and they work just fine.

Anybody? From the error it looks like there may be something wrong in my sip.cfg. The problem happens intermittently, and telling OSS to reload config and reboot phones seems to clear it. But I am stuck.

Weeks later and I still haven’t found a solution. I’m getting to the point of just redoing the entire system from scratch because I can’t kill this bug. Anybody have any ideas?