I wanted to give my information in hopes that it will help resolve the problem. I use Tapatalk on both my iPhone and iPad Mini. End of last week they both stopped working and I was getting the error mentioned in the original post. I got on the board through my computer and saw this post. Here is my current status.
iPhone 5c with iOS v7.0.4Tapatalk v2.3.0 - works fine with no issues that I am aware of.
iPad Mini with iOS v7.0.4 and Tapatalk HD v1.6.1 - when I launch Tapatalk and click on the BYOAC link, the login page comes up and then there is a widow that pops up on top that says "System Message - You are not allowed to login via Tapatalk, please contact your forum administrator." I click on OK and the window goes away and I then have the login page displaying. If I enter my password, I receive the same error. If I cancel the login screen and then click on the link to BYOAC forum again. I am logged in and it works. It's just a little annoying to have to repeat the process.
I am not sure what the reason is, but hopefully this information will help Saint in figuring it out.
Thanks and I really enjoy using Tapatalk to view the forum from my mobile devices.