What Asterisk version are you using? AMI support for Confbridge is only available in Asterisk 10. It does not work in Asterisk 1.8 or older. If you want to monitor conferences with Asterisk 1.8 or older, you must use meetme.
Asterisk 1.8.9.3. After digging around last night I figured that was the case. Our setup is pure VOIP so Asterisk was compiled without support for DAHDI so using meetme is not an option for us. Oh well, not a huge issue.
Thanks.