I'm facing the same hurdle. I opened a ticket with MijoSoft and received the following reply:
"Unfortunately,the problem is with the JFBConnect which does not create users with the normal Joomla standards so you should contact them to fix this issue. You can say them that MijoShop works fine with normal Joomla login so you should fix your code. Also,you can try another Facebook Connect extension for Joomla."
When I pointed out this thread to them, they responded with the following:
"As mentioned in the last message:
www.sourcecoast.com/forums/jfbconnect/jf...t-or-opencart#p29713
The login with the default Joomla/MijoShop works fine. The problem is that JFBConnect breaks this process. You can try it yourself with just Joomla and MijoShop.
I would advice you to press the JFBConnect team and let them check your site and see what is breaking the process. They know their software better than us and can easily see what is the break point."
Is there any chance you briefly touch base with them to set them in the proper direction? I'd private messaged the original poster of this thread and he indicated that they were quite adamant that the issue didn't lie with them and they went to great lengths to try to prove it, rather than to troubleshoot the problem.