Please help!

-- Code by TechicalParadox, 8/2/16
-- Program is meant to run in the background so a remote controller can run any of the commands listed
-- Everything works except where "-- Crashes here" is, the os.sleep(5) and the prints are for testing
-- No error message is listed, I run this program as a bg thread on an advanced turtle and it simply closes at the start of the while loop.

-- SLAVE BACKGROUND PROCESS
slaveControllerID = 1
gotoX = 0
gotoY = 0
gotoZ = 0
gotoPos = nil
updateFreq = 60
gotoUpdateFreq = 15

-- prevent termination
os.pullEvent = os.pullEventRaw

-- initiate rednet
if peripheral.isPresent("left") and peripheral.getType("left") == "modem" then
  rednet.open("left")
elseif peripheral.isPresent("right") and peripheral.getType("right") == "modem" then
  rednet.open("right")
else
  -- no rednet
  while true do -- spin forever
    turtle.turnRight()
  end
end

-- alert slave controller of connection
rednet.send(slaveControllerID, "Connected")

-- communicate with slave controller forever
while true do
  -- send gps location
  x, y, z = gps.locate(1)
  if not x then -- gps failed to locate
    rednet.send(slaveControllerID, "posUnknown")
  else
    rednet.send(slaveControllerID, ("posCurrent"..x..","..y..","..z))
  end
  -- wait for command
  id, message = rednet.receive(updateFreq)
  if not id == slaveControllerID then -- if no message from slaveController
    -- do nothing
  elseif message == "PING" then
    -- respond
    rednet.send(slaveControllerID, "Here...")
  elseif message == "STOP" then
    -- force other programs to stop by rebooting
    rednet.send(slaveControllerID, "Rebooting...")
    os.reboot()
  elseif message ==  "GOTO" then
    -- authorize sending
    rednet.send(slaveControllerID, "Send Coordinates...")
    -- wait for coordinates from slave controller
    id, message = rednet.receive()
    while not id == slaveControllerID do
      id, message = rednet.receive()
    end
    -- x coordinate
    gotoX = message
    id, message = rednet.receive()
    while not id == slaveControllerID or id == SPAID do
      id, message = rednet.receive()
    end
    -- y coordinate
    gotoY = message
    id, message = rednet.receive()
    while not id == slaveControllerID or id == SPAID do
      id, message = rednet.receive()
    end
    -- z coordinate
    gotoZ = message
    print("goto"..gotoX..","..gotoY..","..gotoZ)
    -- tell slave controller
    rednet.send(slaveControllerID, ("Going to "..gotoX..","..gotoY..","..gotoZ.."..."))
    -- GOTO COORD
    curX, curY, curZ = gps.locate() -- get pos
    -- get heading
    heading = ""
    x1, y1, z1 = gps.locate()
    while (turtle.detect()) do
      turtle.dig()
    end
    turtle.forward()
    x2, y2, z2 = gps.locate()
    xD = x2 - x1
    yD = y2 - y1
    zD = z2 - z1
    if xD == 1 then
      heading = "X+"
    elseif xD == -1 then
      heading = "X-"
    elseif zD == 1 then
      heading = "Z+"
    elseif zD == -1 then
      heading = "Z-"
    end
    -- Loop until arrival
    print(heading)
    moves = 0
    print(moves)
    os.sleep(5)
    -- Crashes here
    while ((curX ~= gotoX) or (curY ~= gotoY) or (curZ ~= gotoZ)) do
      os.sleep(1)
      print ("test")
      -- update position
      curX, curY, curZ = gps.locate()
      if moves >= gotoUpdateFreq then
        rednet.send(slaveControllerID, gps.locate())
        moves = 0
      end
      -- Go to proper Y
      if curY < gotoY then
        -- go up
        while turtle.detectUp() do
          turtle.digUp()
        end
        turtle.up()
      elseif curY > gotoY then
        -- go down
        while turtle.detectDown() do
          turtle.digDown()
        end
        turtle.down()
      -- Go to proper X
      elseif curX < gotoX then
        -- go positive x
        if heading == "X-" then
          turtle.turnRight()
          turtle.turnRight()
          heading = "X+"
        elseif heading == "Z+" then
          turtle.turnLeft()
          heading = "X+"
        elseif heading == "Z-" then
          turtle.turnRight()
          heading = "X+"
        end
        while turtle.detect() do
          turtle.dig()
        end
        turtle.forward()
      elseif curX > gotoX then
        -- go negative x
        if heading == "X+" then
          turtle.turnRight()
          turtle.turnRight()
          heading = "X-"
        elseif heading == "Z+" then
          turtle.turnRight()
          heading = "X-"
        elseif heading == "Z-" then
          turtle.turnLeft()
          heading = "X-"
        end
        while turtle.detect() do
          turtle.dig()
        end
        turtle.forward()
      elseif curZ < gotoZ then
        -- go positive z
        if heading == "Z-" then
          turtle.turnRight()
          turtle.turnRight()
          heading = "Z+"
        elseif heading == "X+" then
          turtle.turnRight()
          heading = "Z+"
        elseif heading == "X-" then
          turtle.turnLeft()
          heading = "Z+"
        end
        while turtle.detect() do
          turtle.dig()
        end
        turtle.forward()
      elseif curZ > gotoZ then
        -- go negative z
        if heading == "Z+" then
          turtle.turnRight()
          turtle.turnRIght()
          heading = "Z-"
        elseif heading == "X+" then
          turtle.turnLeft()
          heading = "Z-"
        elseif heading == "X-" then
          turtle.turnRight()
          heading = "Z-"
        end
        while turtle.detect() do
          turtle.dig()
        end
        turtle.forward()
      end
    end
    print("got to end")
    os.sleep(5)
    -- finished goto
    rednet.send(slaveControllerID, ("Finished GOTO @ "..gps.locate()))

  elseif message == "EXCAVATE" then
    -- wait for size
    id, message = rednet.receive()
    while not id == slaveControllerID do
      id, message = rednet.receive()
    end
    shell.run("bg excavate "..tonumber(message))
    -- respond
    rednet.send(slaveControllerID, ("Excavating "..message.."x"..message))
  elseif message == "BURROW" then
    rednet.send(slaveControllerID, "Burrowing...")
    -- go as far down as possible
    turtle.digDown()
    while turtle.down() do
      turtle.digDown()
    end
  elseif message == "ELEVATE" then
    rednet.send(slaveControllerID, "Elevating...")
    -- go as far up as possible
    while turtle.detectUp() do
      turtle.digUp()
    end
    while turtle.up() do
      turtle.digUp()
    end
  elseif message == "UPDATEFREQ" then
    rednet.send(slaveControllerID, "Send new frequency...")
    -- wait for new freq
    id, message = rednet.receive()
    while not id == slaveControllerID do
      id, message = rednet.receive()
    end
    updateFreq = tonumber(message)
    -- respond
    rednet.send(slaveControllerID, ("Frequency updated to "..updateFreq))
  elseif message == "HEADING" then
    -- figure out heading
    heading = ""
    pos1 = vector.new(gps.locate(1))
    while turtle.detect() do
      turtle.dig()
    end
    turtle.forward()
    pos2 = vector.new(gps.locate(1))
    xD = pos2.x - pos1.x
    zD = pos2.z - pos1.z
    if xD == 1 then
      heading = "+X"
    elseif xD == -1 then -- facing -X
      heading = "-X"
    elseif zD == 1 then -- facing +Z
      heading = "+Z"
    elseif zD == -1 then -- facing -Z
      heading = "-Z"
    end
    s = ("Heading: "..heading)
    rednet.send(slaveControllerID,s)
  elseif message == "LOCATE" then
    x, y, z = gps.locate(1)
    rednet.send(slaveControllerID, ("GPS POSITION: "..x..","..y..","..z))
  elseif message == "FORWARD" then
    while turtle.detect() do
      turtle.dig()
    end
    turtle.forward()
    rednet.send(slaveControllerID,"Moved")
  elseif message == "TURNR" then
    turtle.turnRight()
    rednet.send(slaveControllerID,"Turned")
  elseif message == "TURNL" then
    turtle.turnLeft()
    rednet.send(slaveControllerID,"Turned")
  elseif message == "DOWN" then
    while turtle.detectDown() do
      turtle.digDown()
    end
    turtle.down()
    rednet.send(slaveControllerID,"Moved")
  elseif message == "UP" then
    while turtle.detectUp() do
      turtle.digUp()
    end
    turtle.up()
    rednet.send(slaveControllerID,"Moved")
  end
end