Hi Greg,
I'm guessing it might have something to do with the last point mentioned on this link -
http://www.archicadwiki.com/MEP/FAQ
To downgrade to 2325, I believe you actually have to reinstall ArchiCAD afresh and then install hotfix#2 2325 afterwards, as I don't think it's possible to remove a hotfix once it has been installed. You can find the individual hotfixes here -
http://www.graphisoft.com/support/archicad/downloads/
Don't forget to update again afterwards to the latest version!