NOTE: This refers to the standalone 3.x version only. I checked via a search here to see if this issue had been already covered here but found nothing. However if this is redundant to some, mes apologies; but if you haven't used PI in a while, you may find it won't work due to this change -- as I did today, and so I had to get this done.
----- The old and rather clumsy Wondertouch PI activation for both Windows and Mac has now been replaced with a GenArts PI 3.0.9. One has to uninstall whatever one has, then install the new one. Pretty painless. Just be careful with your emitters -- if they are in the default (x86) folder, they may be nuked in the uninstall process. I have mine on my D:\ drive with all my PI projects so all I had to do is reintroduce the shortcut to that folder in PI's default Emitters folder.
Here below is part of the tech support email I got, though all the questions are answered at the FAQ page too.
If you use the Mac version, naturally download and reinstall that one.
~ Philip
"We have replaced the old particleIllusion licensing with our standard GenArts licensing which should require much less frequent reactivations, and also makes it easier for you to move or reinstall a license in the future. You can disregard your old particleIllusion license as we will be disabling it. Please make sure you uninstall particleIllusion from your computer, then download and install the latest version of particleIllusion: