player missing on lineup card...

[fits]

For our region tournament we have 'official scorers' for each game. Official rosters have been turned in before the tournament starts. We use Official Baseball Rules. A lot of the umpires give the lineup card to the scorekeeper to track the changes.
Situation...Later innings of a game, a pinch hitter comes to the plate. Neither manager say anything after the umpire announces the hitter for B7. After a pitch has been thrown, the commissioner of the tournament stops play and states that the pinch hitter is not on the lineup card. The pinch hitter is on the official roster that was handed in before the tournament.
My question is: Who is responsible for catching this error? Is it the HP umpire, official scorer, opposing manager, commissioner, ....
And also, how should this be handled in a game situation?