An impairment of NZ$90 million on an overhaul of the bank's core banking platform has drained the profit of Kiwibank over the year to June 2017. Rumours of difficulty with this project - to replace an Ultradata system on which the bank has relied since its inception in 2002 - have floated for months."A decision has been made to impair the value of the work in progress which currently sits on the balance sheet as an intangible asset," Kiwibank said on Friday.Rumours of difficulty with this project - to replace an Ultradata system on which the bank has relied since its inception in 2002 - have floated for months.Kiwi Group Holdings, which includes Kiwibank, reported a net profit of NZ$58 million, down NZ$73 million from NZ$131 million in 2016.The bank said its underlying profit eased NZ$2 million to NZ$129 million.IT assets "associated with the successful migration of our batch payments to a SAP solution are unaffected," the bank said.Paul Brock, the bank's retiring chief executive, said "a shareholder initiated strategic review is focusing on a number of options for how best to deliver a digital future."Kiwibank said it grew lending to customers by seven per cent to NZ$17.8 billion, while deposits lifted eight per cent to $16.0 billion.