If you have not upgraded your OS to 10.4 Tiger, and have a registered copy of Panther Cache Cleaner and intend to continue using it, do not launch Tiger Cache Cleaner on your computer. I'm not sure how universal and intentional the following effect is, but it has happened on at least my computer and a couple of others I know of. Once TCC is launched, it doesn't accept your old serial number, which is fair enough I guess (though no doubt others will complain about the paid upgrade, as is their right to do). But then PCC won't launch, giving the following message: "This application cannot run on this system. (1039)" TCC not taking my old registration code I can understand. That it seems to "kill" PCC I cannot. I am giving the developer the benefit of the doubt on this, and have contacted him by email asking if there's a solution. I suggest others with the problem do the same. The main thing, though, is that even if you want to try TCC on a pre-10.4 system, I recommend that you don't do it if you wish to keep using PCC, at least until someone has heard from the developer about this.