Hi leoly,
If you want help you firstly have to provide specifics.
ie.
Server
——-
WordPress Version
Apache Version
PHP Version
MySQL version
Versions of all other installed WordPress plugins.
error messages
Client
——–
Platform (IBM PC/MAC etc)
Browser Version
error messages
All
—
Outline of how the error occurred plus steps to repeat it.
We may also ask later for a private email and test site URL and a login but don’t post these here as this is a public site.
Cheers
The Professor
PS. This plugin works fine for WordPress 3.3 -> 3.4.2, PHP 5.2.4 and higher, MySQL 5.0 and higher, and most popular browsers released within the last 3 years. WordPress 3.5 has just been released and this hasn’t been tested yet but should be fine. Some other plugins may cause problems with WP USer Frontend