I'm extremely sorry for the PHP 5.3 requirement not being mentioned on the download page. I fixed that straightaway. Thanks for reportins (and thank Alain for advising me).
The requirement for PHP 5.3 is supposed to show up in the installation screen, but I guess it is too late when you are doing an upgrade (because you already overwrote the code of 18.104.22.168). This is bad thinking from us.
Let's hope new "upgraders" don't get tricked from now on.