Hi Michel,

If you're using the 'enable' line from the controller then I'd suggest not using it and leave the driver permanently enabled instead.
I used it with my home made driver to put the motor into a low power mode. However lots of drivers simply turn off the motor when this is used.

If you're not using the enable line then the issue is with your driver. Some drivers will turn off if there is no activity after a preset time (most modern one's automatically go into a low power state which is ideal). This behaviour may be programmable so check your documentation.

Hope this helps.
Steve.