Problems when running ADPREP32 upgrading old 2000 DC

I have an older 2000 AD network I am upgrading to 2008r2. I know the first step is to run an adprep32 /forestprep on the existing DC.

Keep in mind there USED to be an Exchange 2000 server on this network, but I have removed it entirely from the network using How to completely remove Exchange 2000 or Exchange 2003 from Active Directory which removes the Exchange 2000 org. 

Now when I go to run the adprep32 /forestprep from 2008r2 media on the 2000 DC I get the following error message:

Adprep was unable to extend the schema.

[Status/Consequence]
There is a schema conflict with Exchange 2000. The schema is not upgraded.

FYI, my eventual goal is to bring Exchange 2010 up on another server after I upgrade the domain.

Thanks!