Look for line with Configure::write('debug', 0)
Configure::write('debug', 1) : Errors and warnings shown, model cache refreshed, flash messages halted.
Configure::write('debug', 2) : As in 1, but also with full debug messages and SQL output.
Then errors should be displayed either in your web browser or in your server's error.log file.
Configure::write('debug', 0) : No error messages, errors, or warnings shown. Flash messages redirect.