Permissions problem

Hi,
I created a plugin called Category Manager, that allows wp users to ordre, create, delete and edit categories among other things. It is still in beta version.

A user who tried it informed me that he got the following error message when trying to create a new category:

“You don’t have permission to access /wp-admin/”

I dont quite understand why this happens, since to create a new category, my plugin uses quite the same code as WordPress :

if ( !current_user_can(‘manage_categories’) )
die (__(‘Cheatin’ uh?’));

wp_insert_category($_POST);
wp_redirect(‘edit.php?page=category-manager.php’);

That’s all. Only the redirection changes. Any idea why one might get such an error? Maybe adding
‘require_once(admin.php)’ above this might do the trick. However I have no possibility to test since I dont have the error.

The plugin’s page :

https://www.bidibule.be/wordpress/