Microsoft Corp.'s music and video player Zune, created as a rival to Apple Inc.'s market-dominating iPod, can't share some songs, potentially eroding a key advantage over iPod, Microsoft said Monday.

The company blamed the difficulty on the fact that "wireless sharing is a new experience, and its implementation is in a version 1.0 stage," according to an e-mailed statement. The statement denied reports that record companies such as Universal Music Group were preventing sharing of some artists.

Microsoft introduced the Zune in November, touting its ability to wirelessly share songs and playlists for three plays or three days, a feature the iPod doesn't have. The Redmond-based company has sold hundreds of thousands of Zune players since its release, while Apple sold 21.1 million iPods in the fourth quarter.

"The whole sharing feature was limited to begin with, and the fact that some songs can't be shared even in this limited fashion makes this feature even less compelling," said Michael Gartenberg, an analyst at JupiterResearch in New York. "At a time when they need to find meaningful ways to differentiate themselves from the competition, this isn't going to help."

The company said before Zune's introduction that some songs wouldn't be able to be shared, Gartenberg said. "They never said what percentage of the total songs would be blocked, and it seems a fairly significant percentage of songs people want to share are being blocked," he said.

Gadget blog Engadget reported Jan. 19 that Universal and Sony Music Entertainment were "prohibiting" sharing of works by certain artists. Universal Music spokesman Peter Lofrumento called the report "totally untrue."

"There is no restriction whatsoever."

Microsoft also said the difficulty wasn't a result of demands from music companies. "The issue is not support from our content partners," the statement said. "We've seen broad excitement and support from major and independent labels and publishers."

Microsoft declined to say what percentage of songs can't be shared.

Zune Blog Zunerama found that 21 of the 50 most-popular downloads in the Zune store couldn't be shared, according to a posting Jan. 19. Songs that couldn't be shared included Beyoncé's "Irreplaceable" and Snow Patrol's "Chasing Cars," according to Zunerama.

Microsoft said that it is working to expand the number of songs that can be shared and that all songs copied from a customer's CD collection can be transferred.