His test score was flagged, which means either the NCAA or the people in charge of the test found some reason to question the integrity of the test score. And it might have been a situation where everyone at his particular testing site was flagged, or it could be a matter of his test score improving significantly from the previous time he took it. Scores can be flagged for a few different reasons.
From what I understand, Henderson needed to make a score that was relatively close to the score he previously made to be cleared, and I guess he fell short of that score when he retook the test.