The brush is jammed
Should the red warning light appear as shown (see above picture) the brush jammed warning alarm has activated as the brush bar is not spinning freely.
This is possibly due to a build up of hair, threads and debris around the brush bar. Switch the product off and remove the brush bar:
Remove any build up of debris wrapped around the bristles , also check the ends of the brush bar and remove the end cap to check the bearing for debris. Before re fitting ensure it is free to turn.
Avoid running over rug tassels as these may get caught up in the brush and activate the alarm.