Overvoltage. Probably on the DC bus inside the drive. You may get round this by replacing either a transistor and/or a resistor on the braking circuit.
not real sure where to get the transistors or resistors, but thought I would mention that a guy i know recently got a brand new retrofit drive from Yaskawa that replaced the old SR drives on the Hitachis that he installed himself. He said they called it a Type II. may be worth checking out.
>> Can you provide any more information about this retrofit?
From what I understand it is a new style servopack with the same wiring connections and mounts up exactly the same. The guy I know was told that it was built with parts readily available today so repair and replacement is much easier. I'd call yaskawa for more details since I've only heard about it.