Cause : Motor is turning faster than highest allowed speed due to incorrectly set minimum/maximum speed, insufficient braking torque or changes in load when using torque reference.

Check minimum/maximum speed
settings, parameters 20.01 Maximum
speed and 20.02 Minimum speed.
Check adequacy of motor braking torque.
Check applicability of torque control.
Check need for brake chopper and
resistor(s).