Analysts say the election result is likely to be close
Less than a week ahead of presidential elections in the Philippines, a new vote-counting system has malfunctioned.
But officials from the Commission on Elections (Comelec) said they remained optimistic that problems evident in tests would be solved before the vote.
Computerised vote-counting will be used for the first time in the Philippines in the 10 May elections.
Some candidates and analysts fear the system could make it easier for fraud or miscounting to take place.
There has also been discussion about whether the system's weaknesses could provide adequate cause to delay the vote, although this remains highly controversial.
Some of the 82,200 machines tested failed to read the names of candidates, forcing a recall of the software used, Comelec spokesman James Jimenez said.
"We had some problems with the configuration of the machines. Some of them weren't reading the ballots properly," he told the BBC.
"So we're pulling out all the memory cards and re-configuring them, then we're going to retest them on Friday."
Mr Jimenez repeated assurances that software fixes would ensure that the country's more than 50m voters could vote successfully on Monday.
He said the new configurations would be done over the next few days and that he was "absolutely optimistic that there will be no problems" on election day.
But one analyst told the AFP news agency that the system's problems would "raise doubts about the winners and results".
"This will just increase fears among the public. It smacks of a lack of preparedness, incompetence and their failure to listen and heed suggestions from various sectors," said Bobby Tuazon, policy studies director at the Centre for People Empowerment and Governance.
The 10 May poll is for a new president, vice-president, Congress, half the Senate and all provincial officials.
Benigno "Noynoy" Aquino - the front-runner in a full field of presidential candidates - warned last week that if he does not win he will assume it is because of fraud.
"If we have a correct counting of the votes, I think we will be very victorious," said Mr Aquino, whose mother Corazon "Cory" Aquino took power on the back of the first People Power revolt of 1986 which deposed the dictator Ferdinand Marcos.
If "the people's will is frustrated," however, demonstrations could make this month's protests in Thailand seem "mild" by comparison, he said.
The Philippines has a feisty democracy long marred by fraud, corruption and violence.