There's no timeline for when it will be back.
IRD says it's urgently working to fix the issue.
Inland Revenue's automated system puts more onus on taxpayers to ensure information is correct, a tax expert says.
The new tax rate will take effect on April 1.
Taxpayers don't own their taxes.
A new report found that once again, the average rates in NZ have gone up by $84.
Debate on legislation introducing a rate of 39 percent for people earning over $180,000 a year began on Tuesday.
Labour says it will introduce a tax rate of 39 percent on income over $180,000.
The Greens are proposing a 1 percent tax on net assets over $1 million and 2 percent over $2 million.