Block users from accessing the wp admin area

Hi!

The title says it all. I've created a plugin following the instructions below:
http://www.jasonbobich.com/wordpress/hiding-the-wordpress-admin-panel-to-your-subscribers/

Here's the code I'm using:
http://pastebin.com/2iWVHG1y

I've uploaded a folder named hides-wp-admin-panel with a file of the same name in it, containing the code mentioned above, but users still can access /wp-admin. How do I solve this?

Thanks.