Every criminal file in the New South Wales Supreme Court is being reviewed after an administrative blunder has resulted in a fresh appeal for murderers.

Two of the murderers of Sydney woman, Ms Janine Balding have been granted special leave to take their case to the High Court due to a missing staple from their file. This effectively quashes the pair's unsuccessful appeal in 1992.

The men, Matthew Elliott and "B", who was a juvenile at the time of the rape and murder of Ms Balding in 1988 and cannot be identified, had unanimously lost the appeal along with the third killer, Stephen Jamieson.

Lawyers will argue the failure to staple the Crown indictment to the court file, as required by law, means the pair's case was never "finalized" in the Court of Criminal Appeal. The lawyers also claim none of the laws passed since then, including truth in sentencing, therefore apply to them and they should be released.

Mrs Balding said, "It beggars belief. I can't believe that things happen like this. How do they know someone has not removed the staple on purpose? You can't rely on the law when it relies on a solitary staple."

NSW Opposition Leader Barry O'Farrell today said it was unacceptable that "sloppy bookkeeping'' had led to a fresh appeal.

He told reporters, "A review of Supreme Court rules would ensure these sort of incidents cannot happen in the future."

"We need to modernize our court system, we need to modernize everything around our court system to ensure that sloppy oversights like this cannot result in the possibility of convicted murders being set free."

Opposition legal affairs spokesman Greg Smith said the Government had failed to ensure there were adequate experienced support staff in the state's courts.

He said, "We will be working to get better systems ... I think it is in a mess."

"These type of technical errors should never threaten a sentence that has been properly imposed."

Acting Premier John Watkins said today a registrar with extensive experience in criminal law had already been appointed and was working through the Supreme Court files.

Mr Watkins said, "I'm advised that a full review of every single criminal file in the Supreme Court is currently being carried out, to avoid any repeat of this issue."

"Further, I understand that closing this loophole through an amendment to the rules of the Supreme Court is currently being considered by that court."