2005 gem e4 starts to move in reverse thenstops

No error codes on the display? It might be the dreaded 66 code. When this happens the car might go forward but not backward or vice versa. It can be fixed but it not fun, or you can have the controller rebuilt or you can covert to AC motor and controller.

All this if it is actually a 66 error if not I am not sure where to point you.