I figured it out
The install instructions suggest that for an upgrade to:
(Rebuild Bitfields):
* Goto
http://YOURDOMAIN/admincp/index.php?do=buildbitfields
So, even though mine was a new installation, I rebuilt the bitfields, and now the enabling option appears for my forums.
May I suggest you fix your install directions so that new installations are directed to rebuild the bitfields as well as those doing an upgrade?
Hope this helps the rest of you that are to shy to post that it didn't work when you follow the directions