The Parliament's corporate body said the results of an investigation by the structural engineer of the Stirling Prize-winning were 'hugely disappointing'.
In a report issued to the Parliament last night, Arup said that faulty bolts caused a 4-metre-long beam to swing out of place and dangle over the heads of MSPs. It said it would remove the offending bolt and socket for further investigation.
But Parliament chiefs have slammed Arup's explanation. After examining the engineer's findings for an hour, they said that 'six days after the strut came loose- the onus is on Arup to tell us what went wrong and how to fix it.'
In light of the furore, experts have questioned whether the Parliament should keep its Stirling Prize title.
An academic and an author who has written about the building have both criticised its design credentials in the wake of the incident - the latest in a long line of hiccups.
Peter Wilson, an academic at the school of the built environment at Napier University, Edinburgh, has questioned the appropriateness of Holyrood's accolade.
He said: 'My view has always been that if you give a building an award early you are a hostage to fortune. I think the whole issue of giving buildings awards before they are out of their defects liability period is highly questionable.'
David Black, author of 'All the First Minister's Men - the Truth Behind Holyrood' was more vociferous in his criticism of the iconic building.
He added: 'They should revoke the prize if someone had the guts to ask the right questions.
'There's a safety issue. A foot-tall beam fell out of its fixing. Maybe the MSPs should have got out their instruments and started playing Abide With Me as the ship went down.'
Parliamentary proceedings were cancelled when the laminated oak ceiling beam slipped out of its stainless steel mounting and hung over the heads of politicians. MSPs have been shifted to the nearby venue The Hub until next week.
The Parliament's presiding officer George Reid said: 'Our focus must be to ensure public safety.'
Design expert Wilson said that a large window in the chamber's ceiling exaggerated temperature fluctuations experienced by the roof's metalwork, which could have loosened the beam.
The academic added that if the 'shoes' in which the beams sit had been rotated by 90 degrees the accident could have been avoided.
In light of emerging criticism, Piers Gough, one of 2005's Stirling Prize jury members, jumped to the building's defence.
He said: 'When you do unusual things [with architecture], unusual things are going to go wrong. That's part of life. Someone miscalculated something somewhere.'
Holyrood has been repeatedly criticised after it came in hugely over budget when it was eventually completed last year.
It was also voted one of the British public's ten most hated buildings in a poll ahead of the recently-aired Channel 4 television series Demolition.