BobWeb:
Sounds like you're trying to use an old-format key. You should be using the new-format key - the one I sent on 02 Mar 2004.
(On 01 Mar 2004, an email was sent to all registered Win96 users. That email explained the old vs. new key problem, and invited users to request a new-format key. Most did, but some did not - the "did nots" will have a problem running the most recent version of Win96.)
For people who have merely lost their registration keys... I try to be understanding about this, but I'm actually quite astounded by the number of such incidents. While it's not quite the "100 emails a day" mentioned above, it's pretty high - for every two new registrations, I get an email asking for a replacement for a lost key.
Generating new keys is a manual process that takes quite a bit of time. I generally wait until I have a bunch of such requests stacked up, then sit down for a few hours and go through them all. I do this every three weeks, or so - given the 30-day "trial" period, this shouldn't cause too much difficulty for those who have misplaced the key they purchased.
I'll be processing the backlog of lost key emails later this afternoon. The oldest one I have is from 18 Nov 2005 (23 days ago).