I bought CF Builder back on 8/31. Installed it and I'm fairly certain I entered the serial number for it. But now it just told me that my trial period has expired and it is in limited-use mode. When I select the registration option from the Help menu, nothing happens. What's going on here?
When you start CFB, you'll be confronted with a screen that says your trial has expired (probably the one you mention in your post). On that very screen there's an option to put your registration number in. Put it in. That should sort it.
I dunno why the menu option doesn't work: I've never tried it, TBH.