Human error and failures in management systems have been blamed for the loss of official documents detailing everyone who voted in a crucial by-election.
However, a report released yesterday found there was "no malicious intent" over the disappearance of the marked register after last year's vote in Glenrothes.
An investigation was launched last month after it emerged that the register from November's by-election - in which Labour secured a shock victory - had disappeared from Kirkcaldy Sheriff Court.
Yesterday, Eleanor Emberson, the chief executive of the Scottish Court Service (SCS), said the report revealed "significant failings" in how the documents from the by-election were handled.
She said: "The loss of this important register is unacceptable and I apologise wholeheartedly for the failure to safeguard these documents."
Labour's Lindsay Roy held the Glenrothes seat, which is next door to Prime Minister Gordon Brown's Kirkcaldy and Cowdenbeath constituency, despite predictions that the SNP would win.
When the by-election was over, Nationalists asked to see the marked register - which shows exactly who voted, as officials cross out the names of those who cast their vote at the polling station. However, at the end of January they were told this had gone missing from Kirkcaldy Sheriff Court.
The SCS brought in Bill McQueen, formerly the deputy chief executive of the Crown Office and Procurator Fiscal Service, to carry out an investigation.
Sheriff clerks have had responsibility for retaining electoral records after elections.
Yesterday's report said it appeared to be the first time such documents had gone missing from a court.
The report said: "The investigation has not found the missing records and is not able to determine precisely when and how the documents came to be lost.
"It concludes that a combination of human error and weaknesses or failures in management systems and work processes at the sheriff clerk's office in Kirkcaldy caused the loss."
The report said these included a failure to properly log the documents when they were received.
As the documents were stored in a basement to which outside contractors had access, it highlighted a failure to store the register in a more secure location.
The report makes 11 recommendations, including calling on the SCS to liaise with the Scotland Office and the Electoral Commission to consider the need to issue updated guidance on the handling of records. It also recommends that the sheriff clerk ensure the marked register is stored in a secure location.
Ms Emberson said: "I fully accept the recommendations for the Scottish Court Service set out in this report and will liaise as recommended with the Scotland Office, the Electoral Commission and returning officers on the other recommendations."
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