Originally Posted by Mulholland '49
I never said it contradicted it by Beast building it. It's not going to make any sense if Magneto comes back and helps him build another Cerebro though.
It could be that Erik already helped Charles build a new Cerebro while he was at the mansion in First Class, before they flew off to Cuba.
Otherwise, something happens that means Xavier and Magneto have to work together and desperately need Cerebro to track a mutant.