Auckland Council bungled the amount of money owed by veteran activist Penny Bright, who is facing court action and the seizure of her home over years of unpaid rates.
Papers presented by the council at the Auckland District Court show it was owed more money by Ms Bright than the amount over which it had earlier sought and gained court judgment.
Ratepayers have missed out on $3000 as a result of the error - one of two judgments obtained by the council was for $6500 rather than the $9438 it turned out she owed, the papers submitted by the council showed.
The judgment was one of two, with Ms Bright found to owe a total of $33,000 in unpaid rates and penalties which she was yesterday in court to challenge.
She last paid rates in 2007, refusing to do so since because she says council doesn't adequately explain where the money goes.
She told Judge Mary Beth Sharp the council was in breach of the law when it came to the rates assessment sent to her and every other ratepayer.
She said the law demanded the council explain exactly what it was spending rates money on.
"What I'm looking for is the rule of law to be equally applied. What's fundamental here is these pieces of paper the council sends out to ratepayers all over the region - they need to be legally compliant."
Auckland Council's lawyer, James Hassall, said there was "no dispute the rates are owing". He also said there was compliance with rules obliging the council to explain how rating money was spent.
Judge Sharp said Ms Bright would have a "substantial argument of defence" if she was correct. She said every ratepayer had an obligation to pay rates but the imperative did not "crystallise" until council fulfilled its obligation.
She also told the council its inaccurate assessment of Ms Bright's rates didn't give her "confidence with the integrity of the judgment".
The court hearing rejected Ms Bright's application to have the matter sent to the High Court to find whether council rating assessments were lawful. Judge Sharp said the District Court could decide on the matter as part of Ms Bright's attempt to have the judgments against her overturned.
Having lost the attempt to have the case adjourned, it was put off anyway after documents Ms Bright provided to the court were challenged by council as being incomplete.
Council chief financial officer Kevin Ramsay said the errors with Ms Bright's bill were due to it being a "complex case".