Architecture and Design Scotland (A+DS) - the equivalent to England's CABE - exposed a number of key flaws in the practice's plans for a new visitors' centre during a recent design review meeting.
The centre, which is will be located at Stirling, will mark the position of the National Wallace Monument, completed in 1869 to recognise the bravery of Sir William Wallace.
The revised scheme, which is smaller than an earlier effort, reflects a scaled-back budget, yet is wide of the mark in a number of respects - including a serious lack of disabled access, said A+DS.
The means by which the scheme was presented to A+DS came in for particular criticism. It was felt that the way the structure would reflect on the monument was not properly explained.
The crucial factor, said A+DS, was the lack of decent disabled access to the site. The watchdog deemed this 'not acceptable'.
Their report says there is 'no public step-free access from the building to the road which would then give access up to the monument'.
In the same meeting, schemes proposed for a new campus at Queen Margaret University College in Musselburgh, as well as a draft national park plan were also considered.
Lee Boyd Architects refused to comment.