Drupal: Allowed memory size of X bytes exhausted

First of all, if you're getting this message it means there's something wrong with your PHP.

Use this as a temporary fix to show the error log and fix the issue. Then, make sure to undo this fix.

1- Go to Drupal's root installation and edit index.php
2- Add this function at the beggining of your php code

ini_set('memory_limit', '-1'); 

3- Save changes
4- Clear cache