During Claudelands' first full year of operation the council is expected to have a net deficit of $1.5 million as opposed to the $1.1 million surplus identified in the original budget.
The proposed revised budget will add $2.6 million to the city's books this year and $900,000 for subsequent years until 2022, but the council has said the extra money will be found within its existing budgets and will not result in increasing the proposed rate increases.
Ms Hardaker said the review confirmed earlier fears that the revenue figures were unrealistic.
"I've had concerns it wasn't right. It has given us a good understanding of the situation and a good analysis of what the budget should look like in the 10-year plan."
She was deeply disappointed about how things had been done in the past but didn't want another witch-hunt. Instead, she was relying on Mr Harris to get to the bottom of what went wrong and act accordingly.
Horwath HTL said it was worrying that the already optimistic projections had been increased to 316 and felt 214 events during 2011/12 was a more realistic number. The number of concerts, sporting events and exhibitions had also been overstated.
The review said the business plan was shaky from the beginning because key elements had been left out.
Venue hireage was also priced at a premium and went against advice that they should be competitive in order to win the business. Claudelands meeting rooms were the second-most expensive in the city behind the Ibis, and function rooms were 29 per cent higher than the market average.
Mr Harris said he would investigate why higher figures were included in the last budget. More realistic projections for the 2012/22 10-year plan will be discussed at Thursday's full council meeting.
THE FINDINGS
*Staff influenced Campbell Consulting to increase the Claudelands activity projections by up to 50 per cent.
*Expectations of 316 events in the first year were overly optimistic and have been revised at 214.
*The revenue projections from the business case were increased by up to 11 per cent in the 2009 Long Term Plan.
*Operating costs were reduced by up to 9 per cent in the 2009 Long Term Plan.
*Key recommendations for Claudelands success, including investing spending almost $500,000 on marketing before the centre opening, were ignored.
* The centre is projected to have a net deficit of $1.5 million in the first year and will post a deficit until at least 2014/15.