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Donald Trump and Hillary Clinton won their respective races, both statewide and on Staten Island. (Advance composite)

STATEN ISLAND, N.Y. -- Only about 500 out of 4,566 provisional ballots Staten Islanders filled out in the April 19 primary elections are valid, according to the city Board of Elections (BOE).

About half of the provisional ballots are invalid because the voters weren't enrolled in the party whose primary they tried to vote in.

New York has a closed primary in which only registered Republicans can vote in that party's primary, and only registered Democrats can vote in their party's primary.

Out of the approximately 4,000 invalid ballots, 2,237 were from people not enrolled in the respective party -- the remaining had information missing, the voters were not registered, registered too late to vote or had other errors.

The state attorney general and city comptroller are both investigating the BOE after reports of voter issues at the polls and because of 126,000 registered voters being purged from the Brooklyn rolls shortly before the election.

There were citywide reports throughout the day on April 19 of voters being told they were ineligible to vote.

But BOE officials expected a number of voters to turn up at polls, only to be turned away.

Plenty of people think they're registered with a party, when in fact, they're not, they just typically vote along one party line.

"People are registered as blanks and thinking they can vote," BOE Executive Director Mike Ryan said on Election Day.

Others -- approximately 500 of them on Staten Island -- could legitimately vote in the primary but for some reason their names didn't appear in the rolls or there was some other issue.

Those 500 will be added to the already-tallied votes cast on Election Day.

GOP front-runner Donald Trump and Democratic front-runner Hillary Clinton won the state in their respective races, with Trump sweeping up almost all of the 95 Republican delegates, and Clinton taking home 139 Democratic delegates to Vermont Sen. Bernie Sanders' 108.

Clinton won the state with 58 percent of the vote, but on Staten Island squeezed out a narrow win with 53 percent to Sanders' 47 percent.

Trump won statewide with 60 percent of the vote, seeing massive support on the Island, with 82 percent of the vote.