My game isn’t saving

I started making a game using UE4 and lot’s of it is done already. However, currently, after adding more code to the game, when I tried to save the game, it hasn’t been saving. It says that there is an error. What is the solution to this problem?

What does the error say? You can find out more information in the Output Log (View->Developer Tools->Output Log)

This is how to do game saves, 101: