Isaac Hayes stunned fans at a Stax Records tribute concert in Hollywood on Wednesday night (18Jul07) by mumbling his way through his set and stammering to the audience. The soul man, who turns 65 next month (Aug07), was headlining the 50 Years of Stax concert at the Hollywood Bowl - but his puzzling performance left many fans worrying about his health. Hayes, who checked into a Memphis, Tennessee hospital 18 months ago citing exhaustion, ambled gingerly onto the Bowl's stage and seemed lost at the keyboards during the start of his performance. Later addressing the crowd, Hayes struggled to get his words out, stuttering about a new album he was planning. His lacklustre performance continued, leading many fans to walk out. One Stax devotee says, "It was awful. He just seemed lost onstage. "I went from feeling sorry for the guy to feeling sorry about the money I spent on a ticket to see him perform at the Bowl. There was a mass exodus midway through his set when it became clear there was something wrong." Calls to Hayes' publicist weren't returned at press time. Supporting Hayes at the Hollywood Bowl Stax celebration were Eddie Floyd, William Bell, Angie Stone and Mabel John.