Hi, Franciscus. I'm having that very same problem at the moment, but I just registered at the forums (never had a reason to do it before) and can't send you a PM.
I purchased a FX Interactive physical version of the game (even registered it, so I've got also their digital version, but after I decided to reinstall the game I found out that my serial no longer worked. I can show you my FX digital library as a proof of purchase, as I haven't conserved the ticket.
Maybe I'll be lucky enough so you still read this afer so many years