The University of Hong Kong pollster responsible for Wednesday's constitutional reform poll has blamed a telecommunications company for system errors that emerged at a point well below its server's capacity.
Jazz Ma, information technology manager at HKU's public opinion programme, said an unknown number of people could not vote online in the poll commissioned by the Occupy Central organisers because of the error.
"When the problems arose, the traffic was at a level that the company was supposed to have the capacity to handle. We will have to talk to the company about it," he said.
Because of a confidentiality agreement, Ma did not name the company or reveal its system's capacity. He said he had not thought about seeking compensation although the company had not done its job properly.
A total of 62,169 people cast their votes between 1am and 6pm on Wednesday through a smartphone application, on the internet, or at a voting station in Victoria Park.
To authenticate their identities, online voters had to enter their full Hong Kong identity card number.
They then received an SMS message with an authentication code that they had to send through an SMS to the telecommunications company before they could vote.
"The problem was, many people could not send the SMS to the server," Ma said.
He said the university's system, which could handle 50,000 transactions at once, had maximum traffic on Wednesday of only 7,000 an hour. The university system did not crash.
But errors started to emerge in the telecommunications company's system on Wednesday afternoon, he said.
Ma said the company would look into what went wrong and report back to him within about two days.
In response to reports that pranksters could use someone else's identity card number to vote and that the pollster could not verify whether this had been done, Ma said he and a team of experts had considered different authentication ideas.
"We thought about asking voters to scan a copy of their identity card. But that is too complex and would not work," he explained.
Requiring the voters to fill in the last digit of their identity card number - the "check digit" - should already have deterred some pranksters as random numbers would not work.
Information technology experts believed that the problems encountered during the voting period arose when many voters, who are phone users of a different telecommunications company from the one the pollster used, needed to send SMS messages across networks.
"Something could have gone wrong while the message went across different platforms when many messages were sent at the same time," Francis Fong Po-kiu, president of the Information Technology Federation, said.
IT sector lawmaker Charles Mok agreed, saying that exchanges through SMS messages were often unstable.
Wednesday's survey comprised three questions: whether the nominating committee to pick candidates for Hong Kong's chief executive should be made "more representative"; whether there should be "pre-screening" for candidates, and whether the public should be given the right to nominate candidates.
Watch: Tens of thousands join virtual vote on universal suffrage in Hong Kong