"Add it to the fact that the report sheets are extremely difficult to read, where even I can't even understand where some of this money is coming from."
Overpayment was a big problem in the Western Bay with a number of affected staff giving the money back to their school for "safe keeping" during the Christmas break, he said.
"Overpayment is just as difficult to correct as underpayment.
"I would say this has caused an increased amount of stress and workload in this last week, not just for me, but for other principals and school staff all around the Bay. I'm aware of one teacher at another school being so wound up by all this that she burst into tears," Mr Hyndman said.
Education professionals are set to receive one more payment before Christmas but Mr Hyndman wasn't confident it would go smoothly.
"We're now facing the next big challenge, with teachers getting their holiday pay right up until January 28 ... but it could all go horribly wrong so I'm not holding my breath," he said.
At Tauranga's Kaka St Special School, 13 staff were affected in the last payment.
Principal Barrie Wickens said one staff member was set to be overpaid by $4000, but after complaining to Novopay, the amount was decreased to $400.
"It has been reduced but it's still not correct. This is just another classic example of Novopay getting it wrong," Mr Wickens said.
The school would financially support those who were underpaid, he said.
"This has taken a huge toll on affected staff and caused a lot of stress and worry ... and has put some people into financial stress at a time that's already stressful."
Nearly every school in the Western Bay has been affected by pay inaccuracies since the implementation of the Novopay system in August.
New Zealand Education Institute president Ian Leckie said Novopay problems were endemic throughout the country.
"The Ministry of Education has unleashed a catastrophe and we don't believe this is something that can be sorted this side of Christmas," Mr Leckie said.