Mini MWC: WinGUI works, but arduino IDE failed to flash

[o_lampe]

Hi everyone,
this is my first post here.
I have a mini MW FC from hobbyking, which is connected to the pc through an arduino nano board. The arduino nanos chip is in constant reset status, this way the board should act as a FTDI adapter, right?
With WinGUI everything works well. I have a connection with 115200 baud and I can read and write parameters.
But I would like to flash Multiwii 2.2 with some options enabled. The attempt to flash leads in a AVR Dude timeout error.
For the IDE I've chosen the same COM port and arduino nano is set as board.

What could I try next? Do I need a real FTDI adapter?

[o_lampe]

DOOH,
I read the Manual a few times, before the FC arrived.
I just forgot to use a separate GND probe to put the FC in program mode.