RH9 uninstalled, but can't open old project in RH8

I have Robohelp 8 on my computer. I won Technical Communication Suite 3, which includes RH9, in a raffle, and installed it in a new directory without removing RH8. Then I read that RH9 converts files to a new format that is not backward-compatible with RH8. This scared me, so I deactivated and uninstalled RH9 and all the other components of TCS3. RH8 remains on my computer, and I can launch it normally. But when I tried to open an existing HTML project, I got a message that the project is in a new format that RH8 can't read. So I unzipped a backup copy of the project, but got the same message with it too. I never opened the project in RH9, and I'm pretty sure I never even launched RH9 on my computer before uninstalling it. So what the heck is going on, and how can I go back to using RH8? I hope someone can help me!