VFD: Regenerative overvoltage trip during deceleration or stop
If there is no motor connected, the input voltage must be high or have repetitive voltage spikes that cause the DC bus capacitors to charge to a voltage exceeding the trip point. It is not likely that the trip point is adjustable, but there may be a setting to indicate if the VFD ic connected to 200-208 volts or 220-240 volts. Look at the manual for that. 

If the input power is clean and proper, there could be a failure in the VFD causing this.

A transien voltage condition that frequently causes this type of problem is the ringing transient voltage caused by switching power-factor correction capacitors. The transient only lasts about 2 cycles of the power waveform and doesn't have peak a peak voltage higher than about 30% above the normal line voltage peak. However enough energy can be transferred to the VFD bus capacitors to cause a trip.

A dynamic braking resistor should be connected only according to instructions provided by the VFD manufacturer. An appropriate control circuit is required. Some manufactures have recommended using a dynamic braking resistor for problems of this kind caused by switching power factor correction capacitors. The resistor power rating must be sufficient considering the frequency of switching. It would be preferable to use a capacitor switching method that doesn't cause problems.