I finally got around to looking into this problem again tonight. I think I found what the problem was.
I downloaded the Postfix source code again and rebuilt the package to have quota support. I then reinstalled the packages and all is well.
Perhpas an apt-get upgrade command did something along the way and changed the Postfix packages back to the versions that don't support quota.
I just thought I would post the solution in case anyone else comes along the same problem in the future.
Thanks again for a great community forum.