Server shuts itself down when a player when this player join

I have my own server but it is crashing when this one player joins. I can join and all my other players can but this player that joins and crashs the server is a good friend of alot of people on the server.

NOTE: my server is a tekkit server

If you need mabye a crash thing to help ill try posting one.

hope someone who knows what is wroug see's this