Spain’s government said Tuesday that the massive April power outage across Spain and Portugal that left tens of millions of people disconnected in seconds was caused by technical and planning errors that left the grid unable to handle a surge in voltage.

MADRID (Reuters) -Spanish grid operator Redeia will release its own report on the causes of the massive blackout that hit the Iberian peninsula on April 28, its chair, Beatriz Corredor, told a news briefing on Wednesday.

The Spanish government has said that the national grid operator and private power generation companies were to blame for an energy blackout that caused widespread chaos in Spain and Portugal earlier this year.