After two days of intensive hair-pulling, removing and installing Horde THREE times (all of which garnered no success) I finally concluded that Horde was simply not the webmail solution I needed on Ubuntu 12.04 Postfix/Dovecot.
I opted, instead, for RoundCudeMail which was reasonably easy to install. Only one tricky issue... a pear sql Driver MD2 or something like that which, when you get the error trying to communicate with MySQL, you'll be able to find the driver via Google.
RouncCubeMail is now up and running and simply a much, much easier alternative that the exhaustive process I went through with my Horde experience. Also only two commands to install from the command line instead of the gazillion Horde takes.
Still testing RoundCubeMail but thus far it seems to work just fine.