Until FRS102 basically an error had to be Fundamental for a Prior Year adjustment to be justified
This position is about to change with arrival of FRS 102. Paragraph 10.21 states that ‘an entity shall correct a material prior period error retrospectively in the first financial statements authorised for issue after its discovery’. This means that, on adoption of FRS 102, the threshold for correcting an error by use of a prior period adjustment has reduced from fundamental to material (ICAEW)