[My Server Won't Work]

So my friend and I just tried getting on my server, and I was just on it a few hours ago and everything was fine. Now when we loaded into it, it was like a completely other world. I tried to restore my saved data, but then it said an unknown error occurred. Please I just want to play Minecraft with my friends.

 

["An Unknown Error Occurred" after restoring server to previous version]

I tried getting on earlier today, and my entire world was reset, and I'm not even sure it was the same world from before. Anyone know why this happened?