Java exception thrown

Hi, I'm new to computercraft but not new to programming.
My code is here: http://pastebin.com/v2pUQRpX

local sensor = peripheral.wrap("right")
local chatbox = peripheral.wrap("left")
while true do
  local allPlayers = sensor.getNearbyPlayers(300)
  local string = "!!! INTRUDER ALERT !!! - "

  for key, var in pairs(allPlayers) do
    string = string .. var['player']
  end
  if string ~= "!!! INTRUDER ALERT !!! - " then
    chatbox.tell("Notch", string)
  end
  sleep(1)
end

I'm trying to check if players are around, then tell me when it finds people.
When I run the program it says "java exception thrown" (Yes the peripherals are in the right place).


What's going on here and how do I fix it? Thanks.

An error is occurring within the Java code that makes up the Lua environment. Most of the time scripters encounter this problem when they misuse a peripheral (many peripheral coders don't bother to check input data and generate proper Lua-based errors if it's not sanitised). In this case, I suspect this is your problem - what mod are you getting your sensor from, and do you perhaps need to update it…?