DIAGNOSIS The jar is not correctly detected. The machine has a jar sensing circuit. If it doesn't sense the jar, it stops.
FIX Clean the three metal contact pads on the underside of the jar base and the corresponding contacts on the blender base with isopropyl alcohol. Ensure the jar is seated fully and twisted to the locked position.
IF THAT DIDN'T WORK The magnet in the jar base that activates the reed switch in the blender base may have fallen out or weakened. This requires jar base replacement.
HEADS UP Running the blender without a jar detected can damage the drive coupler and void the warranty.