My friend cannot join the server, when she tries to it says "Failed to synchronize registry data from server, closing connection

I got my server up and running, but only I can join it. My friend cannot join, whenever she tries to, it says "Failed to synchronize registry data from server, closing connection" I just made another world on my server (the one i have right now) and i fixed it, so it isn't crashing anymore but just the same in the world with which such an error occurs, we want to play, because I have already built a lot of things there. My friend has the correct mod list, the same as mine, but it doesn't work for her. And I don't know what to do. Can someone please help me? I really need help. I don't know what to do because i've never been confronted with this error before.I tried to start the server on my own and the connection error appeared when transferring files level.dat and level.dat_old. I have uploaded the log file https://mclo.gs/SDLN7wH