Geeetech I3B single extruder with a second extruder

[Marchello]

I have expanded my Geeetech I3B single extruder with a second extruder which I bought a few weeks ago from you company.
According to me everything is connected correctly. I checked and double checked.
But as soon as I connect the printer to Repetier Host V1.6.2 the log says (among other messages):
FIRMWARE_NAME: Marlin V1; Sprinter/grbl mashup for gen6 FIRMWARE_URL: http://www.mendel-parts.com PROTOCOL_VERSION:1.0 MACHINE_TYPE: GEEETech I3B EXTRUDER_COUNT:1
As soon as I heat up extruder 2 the log says echo: M104 Invalid extruder (see screenshot)
Do I need to upload new software? Because on my original I3B with one extruder the D9 connector was used for an extra fan which worked just fine.
Or am I doing something else wrong?