OK I don't believe I have seen this question before - When I double click the packaged sims 2 pet that I downloaded from Sims 2 Resource, this is what appears: "This package requires Expansion Pack data this is not installed". Now how can this be? I have installed Sims 2 Pets and I have been playing this pets that I have made and even ones that I have downloaded from other sites. But these ones I get this! What do I do?

You need to open it with Pets Bodyshop installer, and it seems as though your game is defaulting to an older version. I found this very problematic in my game- but what you need to do is to right click on a sims2pack, choose open with> choose program and browse to Program files/ EA Games/ The Sims2Pets/ CS Bin/ Package Installer.exe. Hopefully that will make all sims2packs open with the pets installer. However, my computer still refused to do this, so I ended up just dragging the sims2pack I wanted to install onto the Program files/ EA Games/ The Sims2Pets/ CS Bin/ Package Installer.exe icon, and that did the trick. Alternatively, try the Clean Installer.

http://www.modthesims2.com/article.php?t=86150

Ah, I didn't know about that article- however it is incorrect in saying the only workaround is to use the CleanInstaller; dragging the file to the Package installer icon definitely works. I had the Lycos Dog from one of the European websites, and for some reason the dog just would not install correctly with the Clean Installer. I had to use the Pets Bodyshop Installer.

Thank you very much. My computer is doing this and it appears to be working. I will let you know once I get into the game. Thank you again.

Okay, didn't know it was incorrect. I stumbled across that article a couple of days ago.