my worlds do not open anymore, they are all creative and are more important, they are not programmed from beta version 1.8.0.13. The only thing that the worlds have in common is that they all use the / fill of the command_block, maybe that's what made the world inaccessible. I just know, I can not get in, starting game, and I do not play.

It's certainly a bug, because worlds are used for building, and the / fill command makes projects much easier. But the worlds do not open more and as I said, the game closes.

And also the REALMS Minecraft does not work.