Apologies - hope these are just teething issues. When I try to access this page, I get a blank screen. It was working before...is it you or me?? http://dunblanecathbooking.x10host.com/MRBS/
Displaying errors right on the page isn't really a good idea as a visitor can end up seeing information they shouldn't know about. Personally, I go with error logging (where errors get stored in a file) because only you (if you make it 403 on people who attempt to access the log via their browser) can access it outside of the site such as the file manager.
It's your call, really.
Anyway, according to that error, something went a bit off place (literally), that $auth variable of course. A typo most likely occurred. (I generally don't need to comment on this but I felt like doing so to have some relevance here.)