Now subbing for Jack Black (out with a broken funny bone?) in the role of potbellied dork with an unquenchable belief in the power of rock, Rainn Wilson.

He's got the title role in "The Rocker" as Fish Fishman, an unattractive drummer ditched by his glam metal band as a condition of a major label deal.

Fish spends the next two decades in the forced exile of retail sales, and is out of jobs and prospects when he lands a spare room at his sister's place, just upstairs from the band his nephew has formed. When their own drummer drops out just before a big gig (the prom), Fish looms as a last-ditch substitute.

"The Rocker" mines laughs in the potentially deep vein of jokes about an immature 40-something giving how-to-rock lectures to comparatively square teens, with Wilson in the Black-ish role of indefatigable rocker.

Trouble is, "School of Rock," "Tenacious D" and about million comedies of prolonged adolescence have stripped most of the bigger nuggets from this particular seam.

Is there anything new in "The Rocker"? Well, it offers a forum for Wilson's own brand of zaniness - less about the physical energy that Black might have brought to the part, more about Wilson's offbeat way with dialogue.

What both actors share is a willingness to be ridiculous - there's a good bit here about Fish becoming an Internet celebrity when he drums nude during an I-chat jam session, raising the band's profile.

But "The Rocker" is, for the most part, short on these kinds of fresh moments, and plays too often like a retread.

And Wilson is kind of stranded here. His bandmates (including actual musician Teddy Geiger) don't register strongly, and a subplot of Fish's romance with the mother of one of the kids (Christina Applegate) is pretty punchless.

Also not registering strongly: the band's music. Bland, twangy, adolescent laments. The bombast of heavy metal lends itself to funny caricature, the mopiness of synthetic indie rock does not. *