This is weird: despite the CTD I was able to load the save, and it has actually progressed one turn. However, I have received the resources from the Treaty of Altranstädt, but there's no mention of the event in the log. Also my stack that was in Dresden was only moved to the neigbouring province of Radeberg; shouldn't Saxony become neutral and inaccessible?
Before the patch provinces in Courland and Poland changed ownership to Sweden, this didn't happen now. Is it WAD?