The Northern Ireland Blood Transfusion Service (NIBTS) claimed confusion and a "communications" error over the travel criteria for donors prevented those without malaria tests from donating blood.
"NIBTS fully accepts and apologises for the upset and inconvenience caused to those who attended the session and were unable to donate," it said.
Surendran Varma, among the organisers of the blood donation drive, accused the service of turning away potential donors without even checking if they had travelled to India - considered a high-risk country for malaria.
Dr Umesh Vijayam, who also helped to organise the event last year, said people had travelled to Belfast from far away regions of Londonderry, Bangor and Newry in Northern Ireland to take part in what had been planned as a "unique" drive.
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"Around 30 people had already arrived, with many more on their way. One of my friends went in to donate blood, he was very enthusiastic, he was first. They asked had he taken a malaria test since he was from India, a malaria-risk country," he recalls.
A copy of an internal report and staff e-mails from the NIBTS obtained by the BBC through a freedom of information request reveals the service's failure to spot the problem in advance.
A spokesperson for NIBTS claims all donors were assessed individually and some Malarial Antibody Tests (MAT) were taken.
Under its blood donation criteria, if a donor is born in India and spent a minimum of six months in the country, a Malarial Antibody Test is compulsory; if the person has never been a resident, ie just a visitor, the Geographical Disease Risk Index (GDRI) will be referred to in order to assess risk; and if it had been between four and 12 months since their return from a malaria-endemic area, a validated test for malarial antibody must be performed.