You should post a screenshot of the error message. I'm not here a lot, but I know the community is pretty good at helping, when you give enough detail. Without specific messages to analyze, I will say that I've seen this happen myself when the family file is basically corrupted. If you search general help on the EA forums, you will find many similar reports with solutions offered. This is not a DD issue specifically. Generally it's trying to load a family when the save file has been corrupted, for a variety of reasons. Again, it's a common issue with the Sims 4, and you can find help in other forums, too. If you would like assistance here, you will need to attach some screenshots, and whoever is helping you will need some more detailed info like crash logs, last exception logs, etc.