Stormont's finance committee has criticised NAMA's refusal to give evidence on its Northern Ireland loan book sale.
The watchdog said the controversy could be seen as damaging to the reputation of administrations on both sides of the border.
It identified shortcomings in how the Irish Government and NAMA handled the bidding process for its massive property bank.
The committee said it found the refusal of NAMA to attend an oral evidence session particularly unhelpful.
"NAMA needed to be more open and accessible given the importance of the Project Eagle portfolio to the Northern Ireland economy.
"The committee does not accept NAMA's rationale for not attending an oral hearing of the committee, especially given that agency representatives have previously held many meetings with ministers and officials in Northern Ireland."
All parties involved in the €1.5 billion transaction in 2014 have denied wrongdoing.
The sale is also being investigated by the UK's National Crime Agency.
The finance committee report said: "From the evidence to date, the committee is concerned that different aspects of the Project Eagle controversy could be seen as having caused reputational damage to DFP (Department of Finance and Personnel), the Northern Ireland Executive, the Irish Government and NAMA respectively.
"In the case of DFP and the Executive, this relates to how the nominations were made for appointments to the NAMA Northern Ireland Advisory Committee and from the perceptions arising from involvement of ministers with potential purchasers of NAMA-secured assets in Northern Ireland.
"In the case of the Irish Government and NAMA, the available information suggests shortcomings in the handling of the bidding process and related decisions.
"It is therefore imperative that the lessons identified to date are acted on as applicable."
Speaking on RTÉ’s Morning Ireland, the Finance Committee chairman, Sinn Féin's Daithi McKay, said the report criticises Minister for Finance Michael Noonan for not intervening when issues arose.
Mr McKay said this should have happened once it was discovered that there were issues connected to fee arrangements with regard to the sale of the Project Eagle portfolio to PIMCO.
"The issue that we have is that Michael Noonan did not intervene by exercising his general powers of direction over NAMA to suspend the sales process at that point because we have since learned there are very serious question marks over the Cerberus sale - the ultimate benefactor - of the Project Eagle portfolio," said Mr McKay.
"NAMA should have done more. Michael Noonan should have done more, and that was unanimous across all the political parties at the committee in Stormont."
Mr McKay said the decision for NAMA not to attend was not tenable as NAMA had previously visited Stormont to meet ministers.
He said Mr Noonan was also asked to attend.