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You will not be able to install a read-only domain controller in this domain because "adprep /rodcprep" was not yet run

When promoting the first Server 2008 R2 DC in a 2003 domain, I got the following warning:

Active Directory Domain Services Installation Wizard
You will not be able to install a read-only domain controller in this domain because "adprep /rodcprep" was not yet run.

The following was in the error log:     (these are in C:\WINDOWS\Debug\adprep\logs)

Adprep found partition DC=DomainDnsZones,DC=mydomain,DC=local, and is about to update the permissions.
[2011/09/07:15:24:42.609]
Adprep was about to call the following LDAP API. ldap_search_s(). The base entry to start the search is CN=Infrastructure,DC=DomainDnsZones,DC=mydomain,DC=local.
[2011/09/07:15:24:42.609]
LDAP API ldap_search_s finished, return code is 0x0
[2011/09/07:15:24:42.609]
Adprep could not contact a replica for partition DC=DomainDnsZones,DC=mydomain,DC=au.
[2011/09/07:15:24:42.625]
Adprep encountered an LDAP error.

Error code: 0x0. Server extended error code: 0x0, Server error message: (null).
[2011/09/07:15:24:42.625]
Adprep failed the operation on partition DC=DomainDnsZones,DC=mydomain,DC=local. Skipping to next partition.

==============================================================================
[2011/09/07:15:24:42.640]
==============================================================================

Adprep found partition DC=ForestDnsZones,DC=mydomain,DC=local, and is about to update the permissions.
[2011/09/07:15:24:42.640]
Adprep was about to call the following LDAP API. ldap_search_s(). The base entry to start the search is CN=Infrastructure,DC=ForestDnsZones,DC=mydomain,DC=local.
[2011/09/07:15:24:42.656]
LDAP API ldap_search_s finished, return code is 0x0
[2011/09/07:15:24:42.656]
Adprep could not contact a replica for partition DC=ForestDnsZones,DC=mydomain,DC=local.
[2011/09/07:15:24:42.656]
Adprep encountered an LDAP error.
Error code: 0x0. Server extended error code: 0x0, Server error message: (null). [2011/09/07:15:24:42.671] Adprep failed the operation on partition DC=ForestDnsZones,DC=mydomain,DC=local. Skipping to next partition.

The fix was to run the script in http://support.microsoft.com/kb/949257

I had to run the script for both zones that were referenced in the error log. This example is for mydomain.local, make sure to change the parameters for your own environment.

cscript fixfsmo.vbs DC=DomainDnsZones,DC=mydomain,DC=local
cscript fixfsmo.vbs DC=DC=ForestDnsZones,DC=mydomain,DC=local

Then I ran adprep32.exe /rodcprep again, and it failed. I ran it one more time and it succeeded. Now I don't get the warning when running dcpromo.