If Pets is causing trouble with your dynasty file...

[MarianT]

don't despair. I thought I might have lost mine, but managed to get its backup integrated with Pets.

When you get the prompt to "Place lots", click on that. Do not save your game; click on "Just continue."

Place all four lots. Put your dog and cat parks on the smallest lots available because your equestrian center will take the largest one. (I don't know what will happen if your family is living on the largest lot.)

Again, don't save; click on "just continue." You should be able to play.