Role Manager Plugin Fatal Error on changing permissions

I am using wordpress 2.1, I recently installed the rolemanager plugin in wp-content/plugins
The plugin is activated.
When I go to users/roles in the dashboard, I can see the roles and the green or red buttons indicating whether the role has permission or not.
However, when I click to change permissions, I get the following error:

Fatal error: Cannot redeclare class rolemanager in /home/pisspoor/public_html/tabloid/wp-content/plugins/role-manager.php on line 22

I receive the same error when attempting to create new roles.

Its probably something simple…any ideas??

Thanks