Lync 2010 and Group Policy

Hi,

I've deployed lync to some client PCs but would like to use the "Prevent users from running Microsoft lync"

Basically an example of what I am trying to achieve is below:

Install Lync on All Clients

Users need to be added to a group for Lync to Run.  -  G-AllowLync

So i guess what i need to do is Set the "Prevent users from running Microsoft lync" to Enabled on the default domain policy and apply it to all users

The problem is when i create a second GPO with the setting "Prevent users from running Microsoft lync" set to Disabled and apply it to the security group G-AllowLync it doesn't work. the application is still prevented... Im sure this is because im doing something wrong but i can't work out what....? Both the GPO's are linked to the Same OU.