Updated

Sen. Barbara Mikulski (search) tried out a new touch-screen voting machine that was displayed at a local festival and got an erroneous result, an aide said.

Maryland was one of the first states in the country to convert to touch-screen voting (search), which election officials insist are reliable. The $55 million system got a trial run in the March primaries and officials said there were few problems.

But Mikulski learned Sunday the machines are not flawless. According to Michael Morrill, spokesman for the Baltimore Democrat's re-election campaign, Mikulski was at a folk festival when she came across a booth demonstrating the AccuVote (search) TS touchscreen machines.

As she tried out the machines, the senator inadvertently brushed against the sensitive screens, causing the machine to display her vote as a "yes," when she wanted to vote "no," Morrill said.

Morrill, who witnessed the incident, said the foul-up was most likely caused by Mikulski and not the machine. Still, "it showed that, yes, there are potential problems with electronic voting machines," he said.

The machine would have let the senator correct the error by pressing "yes" again to clear it and then pressing "no" again, Morrill said. But she did not do that.

Mikulski did not immediately return a phone call Monday seeking further detail.

Critics of electronic voting machines say the machines are vulnerable to hacking, malfunctioning and other problems.

Mikulski is considering co-sponsoring of a bill in Congress requiring the voting machines to provide paper receipts verifying a voter's selections. Activists in Maryland are seeking a similar state requirement.