Nottinghamshire's Crown Prosecution Service has been criticised for not getting enough guilty verdicts in cases heard by magistrates.
Inspectors from the Crown Prosecution Service Inspectorate assessed the service as "fair" but said it had taken its "eye off the ball".
Cases that were not ready contributed to the high level of ineffective trials, inspectors said.
A CPS spokesman said measures were now in place to improve performance.
Chief Crown Prosecutor Judith Walker said the assessment was not a surprise.
She said the improvements meant the CPS would be "working closely with the police and the courts to try to reduce adjournments, to ensure that cases are ready at every court hearing, and that trials are listed quickly".