Can't get into aether final world codeword "block" after Minecraft update

Can’t load into single player old world of aether_final. The only thing I get is codeword “block”. I did everything suggested to troubleshoot it. Nothing I did works. The only thing I didn’t do was uninstall Minecraft because I have worlds I don't want to lose. But I can make a new world of aether final but, I have gotten so far with this world I do not want to restart from scratch.