Can't get Omeka to display errors

I'm getting the dreaded "Omeka has encountered an error" screen, but with no way to see the error message. Here's what I've done so far:

* Uncommented the line # SetEnv APPLICATION_ENV development in the .htaccess file in the Omeka root dir, in my case, in /var/www/html.
* Restarted Apache with sudo service apache2 restart.
* Restarted the machine with sudo reboot.
* Set the environment variable in the shell via export APPLICATION_ENV=development

Nothing seems to work. How can I get Omeka to display errors?