Chester, West Virginia:Former World Boxing Organisation heavyweight champion Tommy Morrison is staging a comeback, saying on Tuesday that a positive HIV test that ended his career more than a decade ago was inaccurate. "I'm negative and I've always been negative and that should be the end of it," Morrison said. The 38-year-old will face John Castle in a four-round bout on Thursday at Mountaineer Racetrack and Gaming Resort. "The rug was yanked out from under my feet by a misdiagnosis," he said. "All I want to do is fight. ... It's unfinished business." Steve Allred, athletic commissioner for the state of West Virginia, said on Tuesday he approved Morrison's participation in the bout after reviewing medical records and consulting with the Association of Boxing Commissions' medical review committee. Allred said confidentiality laws prevent him from discussing Morrison's medical history or the records he reviewed. West Virginia does not have mandatory blood testing for boxers. Morrison (46-3) and Castle (4-2) square off in one of seven bouts scheduled at the horse race track. Morrison won the WBO title in 1993 by outpointing George Foreman. He lost it later that year. Morrison, who was featured in the movie "Rocky V," also served a couple of years in an Arkansas prison on drug and weapons charges. He announced he had human immunodeficiency virus in February 1996 and last fought in Japan that November, knocking out Marcus Rhode in the first round. Morrison said Tuesday that he has taken several HIV tests while preparing for his comeback and all have been negative. He has signed a contract with Top Rank promoters for at least eight fights this year.