New York-based Warner Music undermined that claim, declaring in a statement that it "has not authorized the use of our content on Qtrax's recently announced service."

Universal Music Group and EMI Group PLC later confirmed they did not have licensing deals in place with Qtrax, noting discussions were still ongoing. A call to Sony BMG Music Entertainment was not immediately returned. Music services such as Qtrax must secure licensing agreements from the record companies, which own the rights to master recordings, and music publishers, which control the rights to song compositions. Each of the major recording companies also operates music publishing units.

Allan Klepfisz, Qtrax's president and chief executive, acknowledged Sunday that the deal with Warner Music had not been signed, but said he expects to reach an agreement on terms "shortly."

Qtrax had been scheduled to make its online debut on Monday, a day after its splashy coming-out party at the annual Midem music business conference in Cannes, France.

Qtrax shut down after a few months following its 2002 launch to avoid potential legal trouble. The company said it latest version of the service still lets users tap into file-sharing networks to search for music. Downloads however come with copy-protection technology known as digital-rights management, or DRM, to prevent users from burning copies to a CD and calculate how to divvy up advertising sales with labels.

The company also promises that its music downloads will be playable on Apple Inc.'s iPods and Macintosh computers until April 15. That's unusual, as iPods only playback unrestricted MP3s files or tracks with Apple's proprietary version of DRM, dubbed FairPlay.

Apple has been resistant in the past to license FairPlay to other online music retailers. That stance has effectively limited iPod users to loading up their players with tracks purchased from Apple's iTunes Music Store, or MP3s ripped from CDs or bought from vendors.

Rob Enderle, technology analyst at the San Jose-based Enderle Group, said he expects Apple would take steps to block Qtrax files from working on iPods.

Last fall, the company issued a software update for its iPhones that created problems for units modified by owners so they would work with a cellular carrier other than AT&T Inc. As a result, some modified phones ceased to work after the software update.

The move prompted antitrust lawsuits on behalf of some consumers.