NORRISTOWN, Pa. -

Charges have been dropped against the former chairman of the Montgomery County Republican Committee, who had been accused of drugging and sexually assaulting a female employee.

Prosecutors announced the withdrawal of charges during a court hearing for Robert Kerns on Monday, based on the fact that the county district attorney's investigative team misinterpreted a key piece of evidence.

Kerns had been charged with sexually assaulting the female employee after giving her wine laced with the sleeping drug Ambien--a  brand name for zolpidem, which is a prescription medication used for the treatment of insomnia.

The charges were dropped because of a misreading of a blood test, said prosecutors.

The test originally showed  Ambien was in the victim's system. However, later readings of the blood test showed no Ambien in her system.

"While the admission of inaccurate information to the grand jury was unintentional, it regretfully happened," said Montgomery County District Attorney Risa Vetri Ferman in a news release. "Upon discovering the issue, my office immediately took steps to investigate, acknowledge and take corrective actions in this matter."

The charges were dropped "without prejudice,"meaning Kerns could be re-charged if more evidence is found.

The district attorney's office is forwarding the case to the Pennsylvania attorney general for review. Attorney General Kathleen Kane has accepted the referral.

Ferman said she will be taking appropriate measures to better protect the integrity of the investigative and prosecutorial arms of her office, through tighter scrutiny of scientific test results and a more extensive system of checks and balances.