The version of the Active Directory schema of the source forest is not compatible with the version of Active Directory on this computer

I currently have a Windows 2000 DC and am trying to install Active
Directory on a Windows 2003 R2 server as an additional DC in the
existing domain.

Using the Windows 2003 R2 installation CD I have run adprep /
forestprep and then adprep /domainprep /gpprep on the Windows 2000 DC
to update the schema but I still get the error :
_________________________________________

The operation failed because:

The Active Directory Installation Wizard cannot continue because the
forest is not prepared for installing Windows Server 2003. Use the
Adprep command-line tool to prepare both the forest and the domain. For
more information about using the Adprep, see Active Directory Help.

"The version of the Active Directory schema of the source forest is not
compatible with the version of Active Directory on this computer."
_________________________________________

Any Suggestions ?

Is the Win2000 schema master set to allow schema modifications?
(http://support.microsoft.com/kb/285172/en-us)

If so, what do you have recorded in the ADPrep logs
(http://support.microsoft.com/kb/309628/en-us)

I'm having the exact same problem. Everything seems ok but I think I must have missed something. adprep /forestprep and /domainprep completed without errors when ran.
The W2K Server is running SP6 + latest hotfixes.
Here's the log from adprep.exe /forestprep(actual domain name changed to protect the innocent). I had to trim some of it because the post was too big...:

Hello! I had this problem yesterday.. Today i discovered that there is a newer versjon of ADPREP.EXE in the catalog \CMPNENTS\R2\ADPREP on CD2 of Win2003 R2!

The version on CD1 will NOT upgrade the schema to version 31!

The version on CD2 fixed the problem :)

I had the same issue when trying to add a 2003_R2_x64 server to a 2003_STD
functional domain. The adprep on disc 2 fixed my problem too... It would
help if their were a KB article describing this situation, but once again the
message board rules!

I receive the same error when try to add a new DC running windows 2003 R2 standard to my existing domain.

My old DC is a windows 2003 standard.

I have not runs any adprep etc since i dont want to mess up my domain.

How can i resolve this?

Thanks for the tip, I checked using the MMC snap in and found I had to
enable "Schema may be modified on this Domain Controller". However,
when I re-run /ForestPrep I get the message :

Forest-wide information has already been updates.
Adprep did not attempt to re-run this operation

Anymore suggestions ?

I ran the utility and got a return code of 30 so it looks as though the
AD schema dis not upgrade. So I guess the question now is how can I run
ADPREP again without getting the error :

Forest-wide information has already been updates.
Adprep did not attempt to re-run this operation

To go from Win 2k to Win 2k3 you run adprep from the Win 2k3 CD. Going from
Win 2k3 to the 2 disk Win 2k3 R2 you need to run adprep from the second disk
of the R2 set.

You should extend the schema by running adprep. Microsoft recommends that
you add the Windows Server 2003 R2 schema updates to your existing Active
Directory installation before you deploy computers running Windows Server
2003 R2, regardless of whether you plan to use these new Windows Server 2003
R2 features or not.

By running ADPREP. It's there for a reason

As stated from the other's adprep from the second R2 disk will upgrade the
schema from version 30 (2003) to 31 (2003 R2), you can check the version
with "schupgr" in a command prompt.

Yes It work
There are many ADPREP. but only from CD2 can fix.