Technical glitches and long queues took the sheen off the first day of early voting in the US state of Florida.
Long queues deterred some would-be voters
The system - used in many other states - was introduced after the fiasco in the 2000 presidential election led to a controversial recount.
Both President George W Bush and his challenger John Kerry are encouraging people to vote early where possible.
But the problems encountered on the first day in Florida have led some to predict a repeat of the chaos.
Any controversy in Florida is set to be particularly acute as it is seen as one of the swing states that could be won by either main candidate.
Whoever wins takes all of the state's 27 electoral college votes - 10% of the total needed to become president.
Mr Bush will be in Florida for most of Tuesday, and Mr Kerry campaigned there on Sunday and Monday.
Florida opened its 15-day voting period without the punch-card machines and ballot papers that caused confusion in the 2000 election.
But problems with computer connections used to confirm voter identities caused problems in at least two counties.
Long queues were reported to have deterred several would-be voters, but they will have until polling stations close on 2 November to have their say in the presidential election.
There have also been concerns - and some legal cases - about the replacement touch-screen machines and the lists of people allowed to vote.
In Palm Beach County, within an hour of polls opening, Democratic state legislator Shelley Vana claimed to have received an incomplete ballot, saying it was "not a good start".
But voter Robin Punches in the county told the Associated Press: "It tells you exactly what to do. It's idiot-proof."
Elsewhere, queues more than an hour long formed.
Lucien Gennaro, a police aide in Coral Springs, had to leave the queue to get to work, and said: "A lot of people who were waiting just left. I'll try again tomorrow. It was a little frustrating
after what happened in 2000."
Mr Bush is to attend at least three election rallies across Florida on a day when new polls gave conflicting opinions on his standing.
A survey for the Washington Post put Mr Bush's job approval rating at 54% and the newspaper reported that, in the modern era, all presidents with approval ratings above 50% have won their re-election bids.
But another poll released on Tuesday for the New York Times and CBS News said Mr Bush's rating was at 44%, which the newspaper called "a dangerously low number for an incumbent president, and one of the lowest of his tenure".
National polls continue to show opinion effectively split between Mr Bush and Mr Kerry, with Mr Bush leading in some surveys.
The Washington Post said though its survey gave Mr Bush a slender lead, Mr Kerry was ahead in 13 swing states by 50% to 46%.