Hi,
The error you posted is not coming form mojoPortal code it seems to be from some kind of installer I'm guessing the ms platform isntaller.
You cannot update/upgrade an existing installation using the platform installer, that is only for new installations.
Upgrading requires manually uploading the files on top of the old files, transfering any customizations from your old web.config file to the new one, then visit /Setup/Default.aspx
Hope that helps,
Joe