You need to give the "assignable to items" permission to a user group for it to be in the list.

I added the 'Assign Resource' permission in addendum to 'Project Administrator' to the default security scheme. There's still nothing to select under Assigned resources.

I would think Project Administration would have full admin rights, is that not correct?

You need to give them the "assinable to items" permission.

I'm sorry, I must be missing something. Can you please be very specific as to where I should be adding that permission?

Go to the Administration -> Permissions page click on the default permission and tick the "assignable to items" permssion at the top, select the group to apply to and click add.

There's no 'assignable to items' to select.

please see screen shot

http://www.patriotproperties.com/permissions.jpg

Sorry, its the "can work on items" permission.

Thank you very much