Key questions over delays to the new Sick Kids hospital in Edinburgh “remain unanswered”, a watchdog has found.
A new report by Audit Scotland said it was not known why errors in the ventilation system were missed.
They also said remedying the problems at the new site and keeping the existing building open could cost NHS Lothian £28million.
“For patients, parents and NHS staff waiting to make the move to the new hospital the picture gets bleaker and bleaker.”
Health Secretary Jeane Freeman stepped in five months ago to halt the opening of the new hospital building.
It was supposed to be in use in July but final compliance checks disclosed the ventilation system within the critical care department was not good enough.
That was despite the formal construction phase for the hospital having come to an end, with NHS Lothian making payments of £1.35 million a month for the building since February.
According to Audit Scotland, a report by KPMG “sets out a picture of human error and confusion over interpretation of the relevant specifications and guidance”.
It added: “At this stage key questions remain unanswered.”
Auditor General for Scotland Caroline Gardner said: “It’s clear that the checks and balances around the construction of the new children’s hospital didn’t work.”
Freeman has already announced a public inquiry will examine issues at the new Royal Hospital for Children and Young People in Edinburgh and at the Queen Eizabeth University Hospital (QEUH) in Glasgow.
Brookfield Multiplex was responsible for the design and construction of Glasgow’s £842million hospital complex.
The same firm is one of the organisations involved in the Edinburgh hospital.
It emerged on Tuesday that NHS Greater Glasgow and Clyde bosses have recommended starting court proceedings against the construction firm amid infection concerns at the QEUH.
Freeman said: “I’d like to thank Audit Scotland for this report, which recognises the crucial role of the independent public inquiry into issues at the Royal Hospital for Children and Young People in Edinburgh and the Queen Elizabeth University Hospital campus in Glasgow.”