I finally got mine working based on the following email from support:

" I have a couple suggestions that might get the HUD working for you, if you want to try them:

1) Export any custom HUD configs and Copy/Paste your \Config folder before deleting any files as a backup.
2) Close HM and the Table Manager.
3) Delete your existing HUD Prefs files, so HM will rebuild them to default.
4) Delete > \Holdem Manager\Config\prefs.xml, pospref.txt, pospref2.txt, pospref4.txt, default.txt, and exenames.txt
5) Start HM< Auto Import, Open the Table Manager, and test on a single cash table.
Windows hides 'known file extensions' by default. :: Scott Granneman

FWIW, my tables were never being found in the table manager window, so if they are being found but the HUD still isn't working, that may be a different problem.