Several students who sat NCEA digital exams last year have been wrongly failed.
The New Zealand Qualifications Authority (NZQA) has become aware of some results where no marks have been allocated.
The affected exams were 2017 digital pilot examinations in Classical Studies, English, and Media Studies, at Level 1 and Level 2.
Relevant schools were being contacted on Wednesday and NZQA is looking into how the error occurred.
NZQA was reviewing any such results and, where marks should have been allocated, the students' record would be updated within the next few days, a spokeswoman said on Wednesday.
NZQA's quality assurance process included checking the marking of a randomly selected sample of digital examination entries, she said.
"These were check marked by a senior marker and no incomplete results were identified through this process."
NZQA had systems in place to ensure "no student is disadvantaged" and encouraged students who had an unexpected zero result in their 2017 Digital Pilot examinations to speak with their teachers in the first instance.
It is not the first time the authority has experienced issues during examinations.
Some mathematics students were in tears after a Level 1 NCEA exam last year, which some teachers said required Level 2 knowledge.
A student who said he was "an all excellence student with a 100 per cent grade point average for all subjects" described the exam as "incomprehensible in parts".
"In some cases calculations were impossible given the lack of information. In others, there were questions not covered in the syllabus."
A Year 11 student at Carmel College in Auckland wrote that none of the work that she had prepared for was in the exam.
"I just wanted to walk out because I had never felt so unprepared for an exam."
That followed another incident at the beginning of last year which saw nervous students unable to log into the NZQA login portal to view their results as the website struggled to cope with the heavy online traffic.
NZQA said an average of 25,000 students were logged into the website every hour.