I "conclude" that based upon what I found, and corrected, in a machine shop last week.
It was actually pretty simple .... nominal voltage (source) 480v, rating of the VFD 400v, and the over-voltage protection set at 500v. Hit the'stop' button and -voila- an immediate 'over voltage' alarm.
The problem was made worse by their using a large resistor, in an attempt to make the machines stop 'instantly.'
It also probably didn't help that the supply was an ungrounded delta.
Moral of the story: Forget DIY and buy the right gear the first time. (For this customer, that applies to the distribution system as well, but that's another story).