It depends on whether it is a handled exception or not as well as what your PHP settings are configured to. You can check your /amember directory for an error.log file and see if there are any clues.
display_errors php setting could be turned Off. Also check error_reporting setting in php.ini as well.
A couple of places can effect this. 1) error_reporting is the PHP value you are looking for defining level of errors that are displayed. For production (non debug) E_ERROR is probably best 2) display_errors allows you to disable displaying of the errors.