The Realms service is experiencing some issues right now, we're working on it, should be back up soon hopefully.
This should be fixed now, sorry for the trouble caused.
That is intended behaviour.
Confirmed in Realms version 1.7.39 for Minecraft 1.8.8
Will be fixed in next Realms client release
Fix will be included in next Realms client release
The client has been updated to not allow uploading of hardcore worlds, you can reset your realm or restore to a previous backup to be able to join again.
Because realms doesn't support snapshots, will be changing the error message however since it's confusing.
Fixed in 1.7.10
Hi, this issue should be resolved now. Sorry for the hassle you had to go through.