Cannot update settings

In the admin panel, Events Manager, Settings….I cannot update the settings.

After clicking Save Changes, I get a 404 page not found and the settings are not updated.

I’m using WordPress 3.6.1.
Events Manager version 5.5.2
Apache version 2.2.25
PHP version 5.3.27
MySQL version 5.1.70-cll
Perl version 5.8.8

WordPress is installed in its own folder with the main index.php file in the public_html root (as instructed by wordpress).

I’ve tried the basics, and still get the 404
1. Deactivated, then reactivated the EM plug-in.
2. Temporarily deactivated all other plugins.
3. Deactivated, deleted, re-added and activated the plugin
4. Tried switching to the default theme
5. Repaired permalinks after each of these steps

The issue stayed the same, with a 404 on attempting to save the settings every time.

Debug gave me the following message when trying to save the settings page:
PHP Notice: Trying to get property of non-object in:
public_html/new/wp-includes/post-template.php on line 29

Line 29 is:
return get_post()->ID;

The URL listed when I am trying to save is:
/new/wp-admin/edit.php?post_type=event&page=events-manager-options#general

I’m using the Customizr theme, however, I switched to the Twenty Thirteen default theme and I’m still having the same problem.

Any ideas on how to solve this problem?

http://wordpress.org/plugins/events-manager/