ORIGINAL: Heliko
I don't have that heli, but it sounds to me like the main gear is upside down, or the one-way bearing has been installed upside down. If the maingear came with the bearing pre-installed pull the gear out, flip the it over, and re-install it.
The bearing allows the rotor system to keep rotating if the motor fails or is shut off. This is what make auto-rotations possible.
...or alternatively, both are in the right way but the motor is turning the wrong direction.