In the latest gaffe in the state’s voter rolls, 1,151 Illinois residents were improperly classified as not registered to vote in next week’s primary before officials caught the mistake.

State election officials sent out letters Monday to local election authorities, ahead of the March 17 primary, alerting them to the problem and telling them to allow the people mistakenly listed as not registered, to vote.

All 1,151 people affected by the problem were attempting to apply for REAL ID, but a spokesman for Illinois Secretary of State Jesse White said he does not know what caused the error, saying it could have been any one of a number of problems.

A spokesman for the Illinois State Board of Elections said he doesn’t think anyone who was mistakenly listed as not registered was inappropriately turned away during early voting, which began last week, since anyone not registered to vote has the option to do so on the spot and election judges are trained to tell people about that option.

“This is our way of making sure that these folks got registered in time for the election,” said Matt Dietrich, board spokesman.

Dietrich said the 87 local election authorities impacted by the error should work to make sure those wrongly classified as not registered are allowed to vote.

People also have the option to register to vote in person at early voting centers or on Election Day.

White’s office could not shed any light on the exact cause of the problem.

“I think we were being thorough in trying to clarify a situation,” said Dave Druker, a spokesman for the office.

Druker said the error, which was first reported by WCIA-TV in Downstate Illinois, is not due to a “computer glitch” and could be a clerical error that may have multiple causes.

Dietrich said roughly 200 registered voters in suburban Cook County, 140 in Chicago, 100 in DuPage County, 80 in Will County, 60 in Lake County, 50 in Kane County and 20 in McHenry County were affected by the error.

For the Secretary of State’s office, it is another mistake in run of recent errors for the office. In January, the Secretary of State office said 545 self-identified non-citizens were registered to vote despite checking “no” on their driver’s license citizenship question. Sixteen of those self-identified non-citizens went on to cast ballots in elections, prompting White to apologize for the error.

”I want to apologize to you and all of those who were impacted,” White told state lawmakers during a hearing on the issue in February. ”There was no effort put forth to hide anything or to cook the books so to speak.”