Keysight RP7970 Serie Manuel D'utilisation page 111

4 Using the Regenerative Power System
can also occur when changing the primary/secondary configuration. Always set the primary unit to
None when changing primary/secondary configurations.
This error also occurs when there is a wrong ac line voltage that has been detected on a secondary unit
that is different than the ac line voltage of the primary unit to which it is connected. Always make sure
that the secondary units are using the same ac line voltage as the primary unit.
Keysight RP7970 & RP7980 Series Operating and Service Guide 111