It seems like the latest version of Zen Cart (zen-cart-v1.2.6d-full-release-with-security-patch) does not seem to support the phpBB2 functionality. I have set it up according to instructions at the beginning of this post and with previous experience. First attempt was to incorporate the support from an initial clean install and then the second attempt was to add support after another clean install.
I have had no luck, there is no option to enter the username required for phpbb support.
If anyone else has experienced differently please let me know.