Federal law requires states to allow voters to cast a provisional ballot if a voter claims he registered before the state's registration deadline and is eligible to vote -- that is, that the voter is a U.S. citizen, 18 years or older and is not a convicted felon (in states that don't allow felons to vote).
http://howto.wired.com/wiki/Vote_(Even_If_They_Say_You_Can%27t)
National Campaign for Fair Elections, part of the Voting Rights Project at the Lawyers' Committee for Civil Rights. "It might be a With the unprecedented numbers of citizens registering to vote for the first time in this election, states and counties have fallen behind in processing registration applications. But even if you haven't received confirmation from your election office, or aren't on the registration list at the polling place, you can still cast a ballot, say legal experts.
"Voters should absolutely be casting ballots if they submitted a timely registration and they are eligible to vote," says Jonah Goldman, director of the National Campaign for Fair Elections, part of the Voting Rights Project at the Lawyers' Committee for Civil Rights. "It might be a provisional ballot, but they should still cast one."
, but they should still cast one."