Polanski, who is under house arrest in Switzerland and faces extradition to the United States, fled the United States in 1978 on the eve of his sentencing for a guilty plea of having unlawful sex with a 13-year-old girl.
Polanski lawyers have been fighting to have the case dismissed, saying the trial judge who had been due to sentence the director had planned to go back on a previously agreed plea deal after improperly colluding with prosecutors.
However in a written judgment released Monday, California's 2nd District Court of Appeal ruled that a lower court had not erred when it had denied an earlier bid by Polanski's lawyers to have the case dismissed.
But the judgment called for an "urgent exploration" of the misconduct abuses alleged by Polanski's legal team.
"Although there is no basis for extraordinary relief here... we remain deeply concerned that these allegations of misconduct have not been addressed by a court equipped to take evidence and make factual determinations as to the events in 1977 and 1978," the judgment read.
"Polanski's allegations urgently require full exploration and then, if indicated, curative action for the abuses alleged here.
"We exhort all participants in this extended drama to place the integrity of the criminal justice system above the desire to punish any one individual, whether for his offense or for his flight."
During a hearing in Los Angeles on December 10, Polanski's lawyer Chad Hummel told three appellate court justices that the filmmaker's case had seen a "record of truly astonishing misconduct."
"It sends chills up your spine what Judge (Laurence) Rittenband was doing," Hummel said, referring to the judge in the initial legal proceedings, Laurence Rittenband, who died of cancer in 1993.
Rittenband's conduct in the case came under intense scrutiny following the release of 2008 documentary, "Roman Polanski: Wanted and Desired."
The film alleged Rittenband was overheard boasting about his plans to jail Polanski "for 100 years" and would not stick to an agreement to give Polanski no additional time after he served 42 days of a 90-day term.
Rittenband's conduct was also criticized by Polanski's victim, Samantha Geimer, who has also requested that proceedings against the director be tossed.
"He didn't care what happened to me, and he didn't care what happened to Polanski. He was orchestrating some little show that I didn't want to be in," she said in the film.
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