I'm having the same issue. I installed Artio Bookit2 on Joomla 3.1..........I get a Global error when I try to make a reservation from the backend:
Error
setGlobalConfigByUserFromReservation(): No user Argument is object, shoul be array
I also get a 500 error when I LOGIN on the front-end or create an account:
Error: 500
TableSubject::bind(*NULL*)
This happens whether I use the Artio user module to login/create account OR if I use the Joomla module. The rest of the website is fine, but when I click on the menu item assigned to ARTIO it kicks the 500 error.