Possible solution to "cannot load this save game. It may have been saved with expansion pack data that is no longer present on this system"
(This solution applies if you know you have the necessary expansion packs installed in your game)
So I might be super late to this and maybe everyone already knows, but I just found a easy fix for this particular save error (especially when installing save files!!)
Here’s what worked for me:
So I installed the world through the launcher, opened my game, and then loaded the world. It seems that if a world is freshly installed in your game (meaning you haven’t loaded it before), you need to let the game generate those files because they contain necessary data required for the save to load. (I'm not sure if the same applies to EP worlds though)
After that I saved my game, went back to the main menu and the error was gone! I could load the save again without issues. 😌