Airport extreme and custom dns setup

I'm having trouble getting dydns setup on my airport extreme using custom dns. I followed these directions: http://www.dyndns.com/support/kb/apple_airport_with_custom_dns.html

I've checked several times and I believe I have the proper setup. Unfortunately, when I do the dynamic global hostname setup with TSIG and update, my airport extreme reboots and never comes up. I can reboot it and it comes back up with no dynamic global hostname. Hence I'm not getting my updates. From some of the messages on this forum I am wondering if it is related to the fact that a PTR record exists for the public IP that AT&T dsl has assigned me. I resolves to an existing hostname.

Is there any way to make this work? If not, am I going to have to get rid of the custom dns and use the regular free service? Can I get reimbursed for the money I spent on getting the domain and custom dns refunded if I have to do this?

Details: Airport Extreme firmware: 7.5.2 Airport Utility Version: 5.5.2 My Mac behind the Airport Extreme is running OSX: 10.6.6

Any help with this problem would be greatly appreciated. I've spent several hours trying to make this work, and would really like to make it work.

Thanks in advance for any help! --keith