LM as ModbusSlave. Transaction ID error

Code:
if not mb then

  require('genohm-scada.eibdgm')

  require('luamodbus')



  -- list of coil mapping, starting from 0

  coils = {}



  -- list of register mapping, starting from 0

  registers = {

    {'40/1/5',dt.float32,0},{'40/1/6',0xFF,1}

 }

  holdingRegisters = {

    {'40/1/7',dt.uint16}

 }

  

  -- list of register data types, element count must match registers table

   

    -- knx group write callback

  function knxgroupwrite(event)

    local value



    -- try to find matching coil

    for id, addr in ipairs(coils) do

      if event.dst == addr then

        value = knxdatatype.decode(event.datahex, dt.bool)

        mb:setcoils(id - 1, value)

      end

    end

    

    -- try to find matching holding register

    for id, addr in ipairs(holdingRegisters) do

      if event.dst == addr[1] then

        value = knxdatatype.decode(event.datahex,addr[2])

        mb:setregisters(id-1, value)

      end

      end



    -- try to find matching input register

    for id, addr in ipairs(registers) do

      if event.dst == addr[1] then

        if (addr[2]==dt.float32) then

          value = knxdatatype.decode(string.sub(event.datahex,1,4), dt.uint32)

        mb:setinputregisters(1+addr[3], value)

            value = knxdatatype.decode(string.sub(event.datahex,-4), dt.uint32)

      mb:setinputregisters(addr[3], value)

            elseif (addr[2]==0xFF) then

            else 

              value = knxdatatype.decode(event.datahex,addr[2])

              mb:setinputregisters(addr[3], value)

            end

      end

    end

  end



  -- coil write callback

  function mbwritecoils(coil, value)

    local addr = coils[ coil + 1 ]

    if addr then

      grp.write(addr, value, dt.bool)

    end

  end



  -- register write callback

function mbwriteregisters(register, value)

local addr = holdingRegisters[ register + 1 ][1]

    if addr then

  grp.write(addr, value, holdingRegisters[ register + 1][2])

    end

  end



  -- knx group monitor, handles group writes

  knxclient = eibdgm:new({ timeout = 0.1 })

  knxclient:sethandler('groupwrite', knxgroupwrite)



  -- modbus slave, listen on all interfaces and default port 502

  mb = luamodbus.tcp()

  mb:open('0.0.0.0', 502)



   --setting slave id is optional

   --mb:setslave(1)



  mb:setreceivetimeout(0.1)

  mb:setmapping(#coils, 0, #holdingRegisters, #registers)



  -- init coils

  for id, addr in ipairs(coils) do

    value = grp.getvalue(addr)

    mb:setcoils(id - 1, value)

  end



  -- init holding registers

  for id, addr in ipairs(holdingRegisters) do

    value = grp.getvalue(addr[1])

    mb:setregisters(id - 1, value)

  end

  

-- init registers

  for id, addr in ipairs(registers) do

    if (addr[2]==dt.float32) then

    elseif(addr[2]==0xFF) then

    else

      value = grp.getvalue(addr[1])

      mb:setregisters(addr[3], value)

  end

  end

  

  -- set callbacks for coil and register write

  mb:setwritecoilcb(mbwritecoils)

  mb:setwriteregistercb(mbwriteregisters)

end



-- handle modbus and knx

mb:handleslave()

knxclient:step()