If you use Blow Up 2 then please check your version number in the about box. On Windows, start Blow Up 2 and open the Help menu to find the about box. On a Mac, start Blow Up 2 and then go to the Photoshop menu to find the about box.
If the version is less than 18.104.22.1682 then you should throw away your old Blow Up 2 installer and download the latest version. Older versions use our old activation system which will stop working for Blow Up 2 on June 6, 2011. Blow Up 2 won’t immediately die, but you won’t be able to do a new installation and activate it.
If Blow Up 2 is working for you then you don’t need to reinstall. But if it ever gives you any trouble (like activation errors) then uninstall the old version and run that new installer. Instructions for uninstalling are below.