I found a fix to this:
Go into the game files, under img/pictures, find Sanura's pregnancy image files. Get Sanurapreg1_stage3_3, make a copy of the file and rename the copy to match the filename the game says is missing (In this case it was Sanurapreg1_stage3_6 for me). Then click retry. Not sure if there are any further missing files, but if you encounter the error again, you can probably fix it by repeating the same thing.
It seems the pregnancy image files were cleaned up from previous releases (Some of them had duplicates), but the game still tries to refer to files that are now deleted? At least it can be fixed easily though.