The command to program the GECKO4Main userFPGA directly via USB is "FPGA_<bitfile>". This command fails, if an inconsistent bitfile is located in the GECKO4com non-volatile
memory during power-on.
At the moment, this problem can be solved as follows:
Erase the GECKO4com non-volatile memory using the "ERASE" command
Power off the GECKO4 Module
Power on the GECKO4 Module
Run the "FPGA_<bitfile>" command