Account Assignment Using Orca and Group Policy

Ok nearly got this working but have one last issue

Im Rolling this out Via an .mst file ceated in Orca

In the Design and deploy option i have ticked " Allow Account Assignment" however if that is ticked it does not assign the account.

If i Untick that the user has an option to allow or cancel, which i do not want i would like it to assign Automatically

How can i do this?