[ForceHSS]

Then, if it is only happening with some groups, then it is a setting in the group causing the problem or some custom plugin. Check under General Permissions in user group manager for each group having problems. If all ok in General Permissions then
Disable plugins via config if this fixes the problem enable plugins again via config, then disable one plugin at a time until you find the problem one

To temporarily disable the plugin system, edit includes/config.php and add this line right under <?php

PHP Code:

define('DISABLE_HOOKS', true); 


To enable plugins again just comment out the line

PHP Code:

//define('DISABLE_HOOKS', true); 


Use notepad++ to edit any files