American Idol received permission to use The Beatles' famed songbook as the basis for one of its sixth season music-genre theme weeks, but due to an inability to find a proper mentor, the show's sixth reason finalists won't be performing any songs from the best-selling and most critically acclaimed band of the 20th century.

"We were in dialogue with them this year as part of one of the genres.  The problem we found -- or the problem we've had, obviously -- is that we need a mentor who's up to the job," Idol executive producer Ken Warwick explained Warwick during a Wednesday conference call with reporters.  "We were after [Beatles producer] George Martin, and his schedule unfortunately... we tried every which way.  We had permission from the record company, we just couldn't get George."

Warwick revealed in mid-January that Idol could use "certain songs" from The Beatles because permission had been granted by Sony, which owns the songbook's publishing rights.  However he told reporters a Beatles'-themed week won't be happening "just yet."

"We were trying to get George Martin to mentor that show -- and you do need a credible mentor if you're doing The Beatles -- and his schedule, I know he was up for it," said Warwick.  "And we got a really nice message from him back saying, 'I would love to do it, but unfortunately I'm in France now, I'm in Switzerland next.  There's no way I can actually be there on the date that you need me.'  And of course, we can't change the date of the show, so it's a very specific day they have to adhere to.  If they can't do it, then they can't do it."

So instead of music by the "Fab Four," viewers got British Invasion week during the Idol 6's Top 11 performance episode, when the finalists were mentored by Peter Noone, frontman for the 1960s rock group Herman's Hermits, and Lulu, a Scottish singer, songwriter, actress, model, and television personality. 

"It's that reason -- and that reason only -- that we went to British Invasion week, which I think was a good week," said Warwick.  "But the fact of the matter is that this is something we don't want to contaminate, we want to do The Beatles in the future, so we'll just wait until George is free and we'll fit it in."

While Martin -- who is commonly known as "the fifth Beatle" -- might seem like the logical choice as mentor because he produced almost all of The Beatles' albums, he is not the most obvious choice in many people's eyes.

"We'd love to have Paul McCartney as a mentor.  Yeah, absolutely," said Warwick.

However while he's unsure "whether it's true or not," Warwick explained "the problem" with having McCartney as mentor is that in the past, he "took exception" to Idol judge Simon Cowell's "comments about the contestants."

"[McCartney's] a nice guy.  He doesn't like Simon saying, 'You're horrible.  You're the worst I ever heard.  You shouldn't be singing,'" said Warwick.  "So the chances of Paul coming on the show were pretty slim."