Frankfurt's police chief Achim Thiel assured the Frankfurter Allgemeine Zeitung newspaper that there had at no time been a security threat, and that information about potential terrorists could be accessed "in other ways."
According to police, a computer error had led to a logjam in the system, and the latest checks of airport security workers had not been carried out adequately. The spokesman said that a slow trickle of new entries had been followed by a sudden torrent of thousands, causing a blockage.
Extra workers have now been brought in to relieve the pressure, he added. This could last weeks or even two or three months.
A spokesman for Frankfurt airport's operator Fraport said that no workers could get onto the airfield, or any other secure part of the airport, without a security check anyway. He added that the fear that there could now be thousands of employees at the airport without valid security clearance was unfounded.
The police's flight safety department carries out security checks on employees in the airport. Employees' data is re-checked regularly.