As stated by
Wikipedia:
The Sims 2 and most of its subsequent add-ons have previously been using Safedisk for copy protection until April 2007. However, since then, Electronic Arts has replaced Safedisk with SecuROM v 7.x software protection, which is included with The Sims Pet Stories, The Sims 2 Deluxe, The Sims 2: H&M Fashion Stuff and The Sims 2: Bon Voyage. Some users have been reporting problems with launching the game, CD-burners or anti-virus protection, due to SecuROM. EA attempted to address some of these concerns on the official website. They instructed users on how to remove the software from their computers.[5] Users who asked about the removal of SecuROM were recommended to not do so, since it can affect the functioning of The Sims 2: Bon Voyage and other EA games that use SecuROM.[6]
I fear that this might be the problem, because I just had a conversation with someone else who is experiencing the same exact thing you are, Katze...
(Anyone can feel free to correct me if I'm wrong, but it is a major public concern with EA integrity at the moment.

I didn't think Deluxe had it on there until I read about it again...)