Error assigning rights

Hi everyone,

I have some trouble with rights. I want to change the rights on one dashboard, si I right-clicked on my dashboard, hit the "Share" button, and added some rights to a role, but when I click "OK", I keep getting the following error :
Access to /pentaho-solutions/myRep/myDashboard.wcdf for operation 32 was denied.

I don't understand since I'm logged in as the super user, joe.

If anyone know how to assign rights to roles for one dashboard, that would be great :)