Answer: When the group's original singer has been dead for more than 30 years and is replaced by a hair-metal refugee with a flair for karaoke (Ian Astbury). Not to mention when the band's first drummer isn't asked to play with them and winds up suing his former friends for millions, a move ­later mimicked by the late singer's estate.

Such were the juicy stories that loomed over the first New York concert in three decades to be advertised under the Doors' banner.

Certainly, the musicians who led this sold-out show at Roseland — keyboardist Ray Manzarek and guitarist Robbie Krieger — contributed immeasurably to what has made this band endure. And no fan was tricked into buying a ticket with promises of a supernatural channeling of ­legendary frontman Jim Morrison. ­People knew what they were getting and seemed to heartily enjoy what they saw and heard, which included more than two hours of Doors' hits.

But to this critic, the proceedings felt like history's first example of a major group reducing itself to its own tribute band.

To invert a famous Rolling Stone headline about Morrison's myth: This show was cold. It was sexless. It was dead.

The necrophilic worship began before a single note was played. A vintage image of Morrison appeared on a video backdrop. Then, singer Astbury (late of The Cult) slunk out in his best Lizard King shades and leather to offer a Rich Little-style impersonation of Lord Jim on "Roadhouse Blues."

Astbury definitely had Morrison's bellow (if not his beauty), and the musicians (aided by a guest drummer and bassist) worked hard to recreate every classic chord and lick.

But even the most rigid nostalgia shows need some ­current intensity. Here, if you closed your eyes, you wouldn't think you were hearing the original Doors. You'd think you were hearing some morbidly studious knock-off act, like Soft Parade.

The group didn't confine their historic worship to the music. They alluded to old court cases as well (including Morrison's public nudity charge). While Astbury made sure everyone ­understood that he's "not Jim Morrison," he did take time out to scream "Jim lives!" while he did his nearest impression.