CHICAGO (CBS) — Some Chicago voters waited in line to cast their ballots until 3 a.m. Wednesday, due to a shortage of election judges and confusion over a new provision allowing people to register and vote on the same day.

Dozens of voters stood in line for more than seven hours at the polling station at Welles Park in Ravenswood, with the last voter casting his ballot at 3 a.m.

The backup was partly the result of a severe shortage of election judges officials blamed on a “malicious” series of robocalls over the weekend, falsely telling Chicago election judges they must go through additional training.

The Chicago Board of Election Commissioners said other judges also were told they must vote a certain way in order to serve as election judge. The calls discouraged some 2,000 election judges from showing up at the polls, and the city had to bring in all 250 standby judges. The city also swore in some voters as judges to allow polling places to open.

“The judges of election run the election in every polling place, and when you have a bunch of them throw up their hands two days before the election, how do you replace them?” board spokesman Jim Allen said.

In addition, some polling places had trouble adapting to a new system allowing voters to both register and vote on Election Day at select locations.

At Welles Park, there were 50 people still in line at 2 a.m., having waited at least seven hours to cast their ballots. At one point, the gym was transformed into a makeshift holding area to accommodate waiting voters.

“It just didn’t seem like there was enough manpower for the demand,” voter Decorda McGee said. “Also, five polling places for a big group of people in a city like this. I mean, it’s just ridiculous.”

Election officials said every ballot cast by the voters who stood in line would be counted.

Meantime, an investigation was underway to determine who was responsible for the robocalls, which Allen called a “dirty trick” apparently designed to interfere with an orderly election, and improperly influence how some people voted.