What happens if you up rpm/v to 400?

There may also be a setting somewhere for maximum motor frequency.

In fact, I've just had a scan of the manual I have and notice the following paramters-
PN020 - Rated speed setting
PN051 - Motor top running speed limit
PN198 - Torque Control speed limit (should only apply in torque mode, but I assume you are using Speed Control mode?)