We now have a KB article 967482 published regarding the NcSecDesc error described in my earlier post.
Dcdiag fails for NCSecDesc test on Windows 2008 Domain Controllershttp://support.microsoft.com/default.aspx?scid=kb;EN-US;967482
Also does this also prevent dcpromo from completing on other DC's?
In my lab DCPromo kept erroring at the point of installing directory data, as soon as I raised the domain and forest to 2008 mode and then ran ADPREP /RODCPREP, DCPROMO worked fine.
Not running ADPREP / RODCPREP command in a Windows Server 2003 / 2008 should not prevent promotion of writable domain controllers in a mixed 2003/2008 or in pure Windows 2008 environment.