When trying to move the Schema Master FSMO role from a 2003 to 2008 R2 server, I came accross an issue. In order to transfer the Schema master role, you need to run the following command:
regsvr32 schmmgmt.dll
Once you’ve done this, you should be able to load the AD schema MMC snap-in, however I kept getting the following error when I ran it.
The module “schmmgmt.dll” was loaded but the call to DllRegisterServer failed with error code 0×80040201
Simple solution to the problem: Run the command from an elevated command prompt, or use the ntdsutil command to do it (But RTFM!)