It sounds like there are other National owners who have a similar problem with the step cover from this thread in the National RV Owner's Forum:
Interior Step Cover 2006 Tropical
You might want to ask over in the National RV Owner's Forum to see if somebody with the same coach may be able to help you or have the moderator move this thread over there.
Also, if you do a search on iRV2, I see there are numerous threads pertaining to step covers malfunctioning on other manufacturer's coaches ...as an example, like this one in the Monaco Owner's Forum:
Step Cover Stopped Working..Please Help
I see other threads in other owner's forums --Tiffin, Winnebago, etc.-- on this problem too. Therefore, as RV Wizzard has said, you may want to take some photos of your cover, where the motor is located, etc.