Hello bowman, sorry for the delay. I got caught up in the last Dell layoff and have been focused on Job Hunting.
I do not hink I can be much help with the php issue for the site. From what I can tell, It looks like a cascading failure starting at UserGroupPromotion.php at line 223 the spurs off to all the other errors listed. Check to see if any recently things changed, like added plugins or new modules added that could throw off the code sequence. If a new plugin was added , turn it off and see if error continues or error changes.
-Jay