Activists staging a massive online Democratic presidential primary ran into some technical problems Tuesday as a flood of Internet voters briefly overwhelmed the MoveOn.org (search) Web site and halted the voting process for more than an hour.

About 50,000 people were able to cast electronic ballots for Democratic candidates on the advocacy group's Web site before the system crashed around 11:15 a.m. EDT.

"We had a much greater load than we expected all at once," said Wes Boyd, president of the MoveOn.org's political action committee, which organized the vote. "We did some tuning and tweaking to make the voting program more efficient, and we anticipate there will be no more problems."

By 12:30 p.m., the site was back up and running, Boyd said.

The primary began at midnight Monday and was to remain open through midnight Wednesday, but Boyd said he would extend the voting period for at least another hour and 15 minutes to account for the glitch. He said the group would send a follow-up e-mail to members who had not yet voted.

The online advocacy group, best known for its efforts to mobilize opponents of the U.S.-led war against Iraq, will endorse the candidate who wins more than 50 percent of the vote and ask its 1.4 million members to donate money to the winning candidate's campaign. Last year, MoveOn.org members contributed $4.1 million to the congressional candidates highlighted on its site.

All nine Democratic presidential candidates are participating in the virtual primary, which is not part of the Democratic Party's (search) official primary process, and have encouraged their supporters to register at MoveOn.org and vote. Boyd expects hundreds of thousands of votes to be cast, with the winner to be announced Friday.

Officials in Howard Dean's (search) presidential campaign said they received several calls and e-mails Tuesday from supporters who got an error message after trying to cast electronic ballots.

"I even had problems when I tried to vote," said Dean campaign spokeswoman Courtney O'Donnell. "When I clicked 'cast my ballot,' it went to a screen that said 'would not load."'

She said the campaign encouraged its supporters to keep trying. The former Vermont governor, who has trumpeted his anti-war views and actively courted Internet-savvy supporters, is widely expected to capture the most votes in the online primary.

Jennifer Palmieri, a spokeswoman for North Carolina Sen. John Edwards' (search) presidential campaign, said she also heard complaints from supporters trying to access the system.

"It's been problematic," she said. "We've heard from dozens of supporters who have either signed up to get an e-mail and haven't gotten it or can't get online or can't get on the site."

While Edwards is participating in the primary, Palmieri played down its importance.

"Any polling more than a year out from the convention has little value," she said.