Upgrade to Windows Server 2012 from Windows Server 2008 R2
@Nev, I had the same error. The Microsoft link suggest to use the Windows 2008R2 disc, however the updates are on the 2012 disc. For me the solution was to perform the Microsoft solution with the Windows 2012 disc and reboot. The same goes for the ADPREP /DOMAINPREP updates.
Just cd to support\adprep on the Windows 2012 media and run:
adprep /forestprep
adprep /domainprep