(In Saturday story, corrects name of company throughout to G4S, not GS4)

(Reuters) - The security company that employed Omar Mateen, the man who in June killed 49 people at a gay nightclub in Orlando, Florida, was fined $151,400 for providing inaccurate psychological testing information on forms that allowed employees to carry guns, a state spokeswoman said on Saturday.

The Florida Department of Agriculture and Consumer Services fined G4S Secure Solutions on Friday after discovering the firm had listed the name of a psychologist who no longer practiced as the screener on Mateen's form and more than 1,500 others over a 10-year period, said Jennifer Meale, a spokeswoman for the state agency.

"It was a clerical error that they were using preprinted forms," she said. "While the forms were inaccurate, we are confident that psychological evaluations were conducted."

Meale said the amount of the fine was the largest on record under this part of state law.

She said the error was discovered following what was one of the deadliest mass shootings in modern U.S. history at the Pulse nightclub after the psychologist on Mateen's background form said she had never conducted his tests.

Authorities believe Mateen, a U.S. citizen of Afghan descent, acted alone in the June 12 rampage, with no help from Islamist militant networks. The 29-year-old security guard was killed by police after more than three hours in the club.

Reuters could not reach Palm Beach Gardens, Florida-based G4S for comment, but the company told the Sun-Sentinel newspaper that an administrative error caused the issue and it immediately acknowledged the error when it was discovered.

(Reporting by Ben Klayman in Detroit; editing by Grant McCool)