James, who was eliminated from the contest at the end of the show, was picked up for his behaviour behind the scenes and singled out for particular criticism by Webber following his rendition of Lady GaGa's 'Born This Way'.
Webber told James that he could not fault his "amazing" vocals, but suggested that the singer was becoming arrogant and would be a troublemaker in a large production.
"I think you need to love the song more than you love yourself," said Webber.
Commenting on James's tweets about his progress in the show, and in particular a retweet of a fan picture that featured the 23-year-old rocker mocked up as Jesus, Webber continued: "Why do you keep tweeting the things you keep tweeting?
"I worry what you're going to be like in rehearsal room with all these big stars. When everyone is going to be equal. I'm having terrible worries.
"Why did you tweet all this nonsense, why did you tweet yourself wearing a crown of thorns?"
James responded at the time with a puzzled look at Webber's comments. Later, he tweeted that he was not surprised to leave the show because it was clear that the West End composer "didn't like me".
Yesterday, James denied tabloid reports that he was acting like a diva backstage and that he had made a member of production staff cry.
"Guys, don't believe all you read," he said. "People don't want me to do well in this show and i wanna really want to," the Berkshire singer told fans.
Ben Forster, David Hunter, Rory Taylor and Roger Wright remain in with a chance of winning the reality show and a role in Webber's rock opera Jesus Christ Superstar.
Superstar continues tonight (July 24) at 9pm on ITV1.