There is a bug in Windows Server 2008 R2 causing a "Bad DNS Packet" error when you try to setup (or promote) Active Directory using Simple DNS Plus and other non-MS DNS servers.
The problem is described in MS KB 977158 - see http://support.microsoft.com/kb/977158/EN-US
The solution is to install the mentioned Windows hotfix.
However the MS KB article only links to the IA64 version of the hotfix - not the X64 version which most people need.
You can get a copy of the X64 version from http://www.simpledns.com/outbox/KB977158-x64.zip
Note that this hotfix will likely be included in a future automatic Windows update and/or a service pack.
So this temporary solution will only be necessary until then.
For more information on using Simple DNS Plus with Active Directory, see http://www.simpledns.com/kb.aspx?kbid=1049