That code would seem not to work with any users who don't have the usergroup as top level.
How would I get this:
<if condition="is_member_of($bbuserinfo,14)">
...to work inside of YOUR conditional?

Usergroup 14 above is my "Premium" group, but I don't put members in their as their MAIN group.
Wrapping the whole conditional I just stated around the "ads for members" section of your code will NOT work. There is a conflict somehow contained in your if if I put my if before it (which has worked before when I simply put the google ads at the top of the showthread before I tried your mod).. Any suggestions?