Whenever he tries joining my friend gets this java.lang.StringIndexOutOfBoundsException: String Index out of range: -1. He is able to join other server far away from his location. There is no explanation for this and help would be great.
lol, string index out of range has nothing to do with physical proximity. Put the whole server log onto Pastebin and put the Pastebin URL in here so we can see the log and maybe figure out what it could be.