NESSUS goes to an activation model
Yep. Starting with build 2.2.1 (2.2.2 is the current build on the Nessus DL site), Nessus now requires you to activate the software. Apparently they have been getting ripped off by a number of folks who are profiting from the GNU product. The good news is that registration is free.
Go to:
http://www.nessus.org/download/
Once you register, you will receive your activation code via e-mail. When Nessus finishes installing, it will prompt you for the code. Once you enter it, you can use Nessus as you always have in the past.
Anyway, FWIW.
--TH13