error installing Exchange 2010 "cannot find Exchange administrative group"

Hello support,

I get the error "Could not find the default Administrative Group 'Exchange Administrative Group (FYDIBOHF23SPDLT)".

I understand to correct this error I can run "setup.com /prepareAD /Forest /Domain" etc to update the schema and correct this issue.

I have the most current ISO from microsoft for Exchange 2010 SP1 and my schema is NEWER than the ISO thus running setup.com does not change this issue as the update of the schema fails.

How can I update my schema outside of the current ISO from microsoft?  Is there an alternate method that I'm not aware of?

Any help will be appreciated, thanks!