Trial

I downloaded the 30 day trial of NIS 2011. It has now expired. I then found a offer for NIS 2011 60 day trial. I uninstalled my 30 day trial and then installed this 60 day trial. It still says "expired". Why is this? Is this normal? Can you just keep on uninstalling and reinstalling the 30 day trial? I dont think so cause its stored in the registry. I also found a 90 day trial from ING. Can I use that? None of them come with a serial number so I imagine everything is stored in the registry. Thanks. Please do not make rude replies. I also searched the forum and could not find anything related to this topic.