Libra is a key part of the government's Exchange project to link systems in criminal justice agencies, which was due to start going live next month.
A spokeswoman for the Department for Constitutional Affairs, which is managing the Libra project, said last week that testing the system's performance would continue throughout November and a decision would then be taken on what to do next.
In September Computer Weekly reported that the fourth attempt in 15 years to build a unified case management system for magistrates courts had run into delays because of bugs and application speed problems.
In a statement, the department said, "[The] underlying architecture of the new Libra application is based on proven scaleable technologies - Java, Oracle, Oracle RAC and Linux - and the testing under way is intended to give us the necessary level of confidence in the system to allow us to press ahead with deployment." It added that it would "only roll out a system to the courts that is fit for purpose".
In June, Paul Atwell, director of Libra, wrote to Justices' chief executives, who run the administration of magistrates courts, saying, "The overall project remains very much on track."
But his letters since then have warned of technical challenges and a delay of three months in the roll out of Libra. In the latest letter to 42 Justices' chief executives, dated 25 October, Atwell said there had been a "delay in deciding and confirming the revised roll-out timetable".
He added,"There is still work to be done on confirming the application's ability to function efficiently over a large network - its scalability." This work involves monitoring the application in a test environment that simulates the high volumes of users and data it will need to handle.
Until Atwell has a "very high level of confidence in the application's scalability", he "cannot confirm the current roll-out timetable, which therefore remains provisional for the time being".
With some courts having prepared to go live in January 2005 - including the recruitment of specialists into Libra-related roles - Atwell said he appreciated the effect of the uncertainty. "Rest assured that the project continues to be managed for success," he said.