Did you Reboot after the uac disable? If not, please do before proceeding.
Are you running the Preinstaller on a machine with Exchange Command Shell in an Exchange 2007 or 2010 environment?
if yes so far, not sure why, but there are two solutions: Go get some more coffee
Then you can manually make your A2E Service account "zadd2exchange" in whatever unmanaged "service account" type OU you wish from within Exchange Management Console
Then rerun the Preinstaller again and make sure the name of the account is correct, then select the checkbox that account exists
Next, make sure the service account is part of the local administrators of the machine you are installing it on and any Exchange Server you are talking to or are replicating to including DR (usually all of them).
Then Log off and back on as the A2E Service account and run the CDO mapi install (if not on the same machine you ran the preinstaller) from the Preinstaller Dir, then go through the installation again. If CDO asks to upgrade, do not do it. Stop, uninstall the old and then install the new.
This should do it.