[Question/Error] parallel API

--[[
chat system client
© 2013 InputUsername
please don't copy/redistribute/use this code
it's only here because I need to get an error fixed
]]

local chat = {"Welcome to chat!","Commands: /leave"}
local sLocalName, nServer

rednet.open("top")

local function getMessages()
  ev,id,msg = os.pullEvent("rednet_message")
  if id == nServer then
	msg = textutils.unserialize(msg)
	if not (msg == nil or msg["name"] == nil or msg["msg"] == nil) then
	  table.insert(chat,msg["name"].."> "..msg["msg"])
	end
  end
end

local function drawScreen()
  term.clear()
  term.setCursorPos(1,1)
  if #chat <= 16 then
	for i = 1, #chat do
	  print(chat[i])
	end
  else
	for i = #chat-17,#chat do
	  print(chat[i])
	end
  end
  term.setCursorPos(1,18)
  print(string.rep("-",52))
end

local function sendMessages()
  term.setCursorPos(1,19)
  term.clearLine()
  term.write("> ")
  local send = read()
  rednet.send(nServer,textutils.serialize({name=sLocalName,msg=send}))
end

term.clear()
term.setCursorPos(1,1)

print("Insert desired username:\n")
print("Insert server id to join:\n")

while (not sLocalName) or (not nServer) do
  term.setCursorPos(1,2)
  term.clearLine()
  sLocalName = read()
  term.setCursorPos(1,4)
  term.clearLine()
  nServer = tonumber(read())
  rednet.send(nServer,textutils.serialize({name=sLocalName,msg="/join"}))
  id,msg = rednet.receive(5)
  if id == nServer and msg then
	msg = textutils.unserialize(msg)
	if msg["name"] == "server" and msg["msg"] == "/ok" then
	  break
	elseif msg["name"] == "server" and msg["msg"] == "/double" then
	  sLocalName,nServer = nil,nil
	end
  else
	sLocalName,nServer = nil,nil
  end
end

while true do
  parallel.waitForAny(getMessages,drawScreen,sendMessages)
end