I have not played the Sims 2 in a while -- but when I wanted to, some weird error appeared:
"A required security module cannot be activated.
This program cannot be executed (6000)."

I have custom content installed on my laptop, but this error has never appeared before. I re-installed the game and everything worked perfectly, without the custom content. Now I downloaded some hair from this site, just to test if the error appears again. I installed one of the files, and boom! The error appears again.

What is this and how can I fix it?

This happened to me today as well. I downloaded a mod and went to open the game and received the same error code. I went back to my downloads folder and deleted the files from that particular download, before trying to start the game again. This time it started right up... no error. Could there be a problem with DLC on the site? All my other mods/custom content work fine still.

Are you using the Launcher? What happens if you run the game without it?
http://simswiki.info/wiki.php?title...assing_Launcher