MODBUS TCP SLAVE

[palomino]

I have this exmple the modbus tcp slave.
But when I try to read the log I get an error.
why?

this is the type error that have 

* arg: 1
  * string: read failed
* arg: 2
  * string: Bad file descriptor

Code:

require('luamodbus')

if not mb then
   mb = luamodbus.tcp()
  end

  mb:open('0.0.0.0', 502)
  mb:connect()
  mb:setslave(2)
  mb:setmapping(1, 1, 3300, 1)
 
  function setint64(grpaddr, regaddr)
    local value = grp.getvalue(grpaddr) or 0
    local raw = knxdatatype.encode(value, dt.int64).dataraw
    local r1 = raw:byte(2) * 0x100 + raw:byte(1)
    local r2 = raw:byte(4) * 0x100 + raw:byte(3)
    local r3 = raw:byte(6) * 0x100 + raw:byte(5)
    local r4 = raw:byte(8) * 0x100 + raw:byte(7)

   val, err = mb:setregisters(regaddr, r4,r3,r2,r1)

end

  function updateregisters()
    setint64('32/1/1', 3204)
  end


  updateregisters()
 
val, err = mb:readregistervalue(3204, 'int64', 'b')
log (val,err)

  if val then
    log('read ok', val)
  else
    log('read failed', err)
  end