Can't walk beyond a certain part of a world on my server.

So, I run a small Minecraft server for me and my friends. One day, the server would start kicking people that walked past certain point in the town. It seems this is due to a string being too big. The errors from the server and the client are in the picture that will be sent with this report, if you need, I can send you the world or anything else you might need. Please fix this or tell me a workaround, thank you in advance.