I am currently having the same issue as well. Tried to upload a custom world to my realm and it gave me the same error message. I re-downloaded the map file thinking that it might be corrupt but works fine in singleplayer.
Ian Elliott
I am currently having the same issue as well. Tried to upload a custom world to my realm and it gave me the same error message. I re-downloaded the map file thinking that it might be corrupt but works fine in singleplayer.