mcd2230 does not responde after firmware update

the MCD2230 does not responde to any communication after firmware was updated over dfu
the red status led stays on and the usb led stays off and the rs232 communication only shows: 'starting...'
and new firmware cannot be reuploaded through rs232 it give the fault message ;
'checking firmware... error.
new firmware message not detected''
it also cannot connect to dfu mode

what to do?