Hello HotPot people!
Over the last few days, I have realized a mistake I made in the version numbers of "HotPot v2.0", which is the HotPot module in Moodle 1.5. To my dismay, the version number for "HotPot v2.0" had overtaken the version number for "HotPot v2.1", which is the HotPot module in Moodle 1.6. Yikes!
So today, I sat down and sorted it out. Everything should be OK again when you upgrade from Moodle 1.5 to Moodle 1.6. The update script for the HotPot module should trigger correctly, and the HotPot tables will be adjusted as they should be.
A happy by-product of this testing is that the "HotPot v2.1" module is again compatible with all Moodles, from Moodle 1.6 back to Moodle 1.1.1 
If you want to download "HotPot v2.1", you can get it from my server:
http://bateson.kanazawa-gu.ac.jp/moodle/hotpot-module.2.1.x.zip
Please note that the version of the HotPot module that is available on the Moodle downloads page is "HotPot v2.2", which is intended for Moodle 1.7 ONLY and is NOT compatible with any earlier versions of Moodle.
This problem with the version numbers may have been part of the cause of the difficulties that Mandy H. and John H. have reported this week. I apologize for my part in your troubles 
If you have not tried to upgrade your HotPot module recently, this version problem that I am talking about has not affected you, and will not affect you if you upgrade your HotPot module or Moodle site in the future.
thank you all for using the HotPot module and sending in your feedback
Gordon