Took a little while but here is what I found.

506 (Error) DNS_EVENT_INVALID_REGISTRY_PARAM
The DNS server has invalid or corrupted registry parameter %1. To correct the problem, you can delete the applicable registry value, located under DNS server parameters in the Windows 2000 registry. You can then recreate it using the DNS console. For more information, see the online Help.

To correct check out the fllowing link.

http://support.microsoft.com/support/kb/articles/Q282/9/24.ASP

You will want to perform the RESOLUTION step "To correct the DNS forwarders settings in the registry:"

Cheers.