I believe that 500 Error was already fixed (your bug report in github), so I'll just make some comments regarding this topic..
In my opinion JomSocial API is much better than in most Joomla software -- at least they have an API. For example API in Kunena 1.7 is very basic and limiting. I'm happy to say that this will change in 2.0, where we have pretty good framework that is used also by Kunena itself.
In general -- let's not blame other products in our site as probably our software is as bad as the others are -- for some users. All software has bugs and some of them are really hard to track down, especially if they cannot be reproduced by anyone in our team.
You can also sell GPL software -- you just need to give source code to everyone who buys it and you grand them permission to do whatever they want to do with it (well, almost).
Kunena will always remain free and open, but there might be some paid templates, add-ons or plugins offered from the team for those users who need more than the normal features. Selling just support is too much work for too little money, so there must be something else to offer, too. Otherwise we'd just use all our time by supporting the product and the product itself doesn't evolve.
PS. You can apply to our testers team (JomSocial group).