Irish-American voters hoping to vote in this week's Michigan Democratic primary were facing huge disruption because of an error in the voting registration programme which is rejecting names beginning with prefixes such as "O" and "Mc".
The Democratic Party has admitted that its system was rejecting thousands of voters who had surnames such as O'Connor or McNamara.
The electronic glitch occurred because the party's computer programme had problems identifying an "embedded gap" between the prefix and the rest of the surname. Names such as O'Connor and McNamara were recorded as Connor and Namara, and so legitimate voters intending to vote for a presidential candidate were not being recognised.
The problem first surfaced last Saturday when the Howard Dean and John Kerry campaigns encouraged thousands of people to register and the party's computer programme incorrectly recorded voters names.
Democratic political analyst Mr Mark Grebner said that the about 15 per cent of all Democratic voters in Michigan had been denied a vote.
"That's not all from this problem, but it has been very significant," he said. "It has mostly affected Irish, Dutch and Arab Americans because they are the one's mostly likely to have a prefix to their surname."
Mr Grebner said he had received many complaints from Irish American voters but was satisfied that the problem was under control.
"Discriminating against Irish Americans in a place like Michigan is not a smart thing to do, so it shouldn't have happened in the first place" he said.
Michigan Democratic Party spokesman, Mr Jason Moon, said the problem had been rectified this week. Mr Moon said the problem was caused by an electronic programme's interpretation of the Michigan Secretary of State's qualified voter file.