So the system with the problem is a server to which I don't have root access. Which unfortunately means that I can't re-install Perl :( But I'll talk again with the admin and see if he can find a time window at which he can re-install Perl (quite a few other people are using this server).

Also, while I could agree that the script's code isn't good enough, or that I should use threads instead of forks, the thing is that this same script runs fine on another machine!

Many thanks for the help guys! Really appreciated!