The Back-Up Plan, Jennifer Lopez's latest romantic comedy, opened this past weekend and grossed a lousy $12.3 million—and ably described what Lopez desperately needs right now, career-wise. This latest bomb cements a professional plummet that threatens to make one of the biggest stars of movies and music over the past decade little more than Mrs. Marc Anthony.

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At the height of her career, between 1997 and 2002, when she rolled with Puffy or Ben Affleck and a posse a dozen deep, Lopez made up to $12 million per movie. During this period, she made nine films, which grossed between $24 million and $94 million domestically. Since then, The Back-Up Plan has been more typical, in the mold of Gigli and An Unfinished Life, which collected an unrespectable $6 million and $8 million, respectively.

Lopez's music sales mimic that trajectory. Lopez stormed on to the Billboard charts over that same period, releasing four albums that sold a combined 10.7 million copies, according to Nielsen SoundScan, and providing her a $5 million per album deal at Sony, says a source close to that deal. Her three subsequent releases barely cracked 1 million copies in total—a stunning collapse that can't all be attributed to an overall decline in CD sales—and her latest single, "Louboutins," an ode to shoes that cost more than most people's rent, flopped at radio.

"If your pitch has been 'Jenny from the block,'" says one person whose music-related company has done business with J. Lo, "you don't do a song about $700 shoes. Know your demographic."

"If your pitch has been 'Jenny from the block,' says one person whose music-related company has done business with J. Lo, "you don’t do a song about $700 shoes. Know your demographic."

All these bombs have shaved millions off Lopez's going rate. Sources say that she banked between $4 million and $8 million for The Back-Up Plan, or between one-third and two-thirds less than what she was previously making per film. On the music side, her Sony deal ended in February, and her impending deal with Island Def Jam will guarantee her less than $1 million per album, with the chance to earn more only with strong sales, according to a source with knowledge of those negotiations. It's basically a deal that puts all of the risk on Lopez—if her album tanks, she loses face but the label doesn't lose much; if it's a hit, then she will rightfully cash in, as will the label.

A representative for Lopez did not return a request for comment. Representatives for Sony Music and Universal Music Group, Island Def Jam's parent company, declined to comment. But the numbers speak loudly: to the entertainment world, Lopez is again viewed as an unproven entity, someone that needs to be discovered by the public all over again.

Perhaps that's why Lopez decided to reteam with her former manager, Benny Medina—which some sources consider a big mistake given an extraordinarily difficult reputation.

"When people's careers begin to falter, they reach out to the person who they once fired, forgetting the reason they fired them in the first place," says a source with business ties to Lopez. "I think that's what happened with Jennifer and Benny. He's not responsible for her film career, he's a music guy, so she reached out to him to try and relive those days of success and the problem is that the record business is dramatically different than it was when she released her first album."

Another problem is that the promotion costs for a star of Lopez's stature are enormous, but come with diminishing returns in an era where fewer and fewer people buy albums. A second source who worked with Lopez when she was at Sony says the label spent between $2 million and $3 million on her last record. Band rehearsals can cost upward of $150,000 per session, and "glam squad" costs, or the money spent on makeup and clothing for television appearances, can run from $50,000 to $75,000.

"She's an expensive proposition," this source says. "She's a superstar talent, but she doesn't have a touring base and doesn't do well in merchandise sales, and that's where the money is in music these days."

According to two other well-placed sources, Sony expressed some willingness to keep Lopez at the label, but not with the perks and marketing to which she was accustomed. In the end, the two sides decided to end the relationship.

Lopez does have other sources of income besides movies and music, among them a fragrance line, clothing line, and restaurant. But these businesses aren't big revenue generators—for instance, a fragrance industry source says Lopez received between $500,000 and $1 million upfront for agreeing to license her name to Cody for a perfume line, as well as a percentage of sales. (A Cody representative could not be reached for comment.)

Moreover, these businesses have suffered in proportion with her slumping movie and music career—hits in those arenas drive ancillary product sales. For example, her first perfume, Glow by J. Lo, ranked as not only the bestselling celebrity fragrance, but also the second bestselling fragrance in any category behind only Chanel No. 5 when it debuted in 2003. Since then, however, each subsequent line of perfumes has failed to reach the sales level of the original, which the fragrance industry says sold several million dollars worth of bottles worldwide.

Always a fiend for fashion, J. Lo made a splash on the Grammy red carpet in 2000 when she appeared famously clad (or not) in a cleavage-baring Versace gown. At that time, she was a cover-worthy hot commodity with a tumultuous love life to match. She scored a much-coveted Louis Vuitton advertising campaign in 2003, an endorsement of her value and fashion-icon status, and launched a clothing line, Sweetface, which did solid numbers at retail initially.

But the line lacked an identity, and had little to do with her "Jenny from the block" past, nor her high-voltage transformation. Plus, it didn't help that she was hardly ever photographed wearing the clothes (unlike, say, Victoria Beckham, who is a walking billboard for her line). Last year Sweetface closed up shop.

Now along with marriage and motherhood, J. Lo finds herself reduced to intimate sit downs with the likes of supermarket tabloid Us Weekly, whose cover last week bared the mundane tagline: Jennifer Lopez talks baby weight battles, her stay-sexy secrets and life with the twins.

My how things have changed.

Jacob Bernstein contributed to this story.

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Peter Lauria is senior correspondent covering business, media, and entertainment for The Daily Beast. He previously covered music, movies, television, cable, radio, and corporate media as a business reporter for The New York Post. His work has also appeared in Avenue, Blender, Black Men, and Media Magazine, and he's appeared on CNBC, Bloomberg, BBC Radio, and Reuters TV.