People who have bought music from Microsoft's MSN Music store could face problems if they decide to buy the firm's new Zune portable player.
Zune hopes to steal customers from Apple's iPod and iTunes
Microsoft has said it will stop selling music from MSN music from 14 November, when Zune goes on sale in the US.
But in a move that could alienate some customers, MSN-bought tracks will not be compatible with the new gadget.
The move could also spell problems for the makers of MP3 players which are built to work with the MSN store.
Slice of the action
The problem has arisen because tracks from the MSN Music site are compatible with the specifications of the Plays For Sure initiative.
This was intended to re-assure consumers as it guaranteed that music bought from services backing it would work with players that supported it. MSN Music, Napster, AOL Music Now and Urge all backed Plays For Sure as did many players from hardware makers such as Archos, Creative, Dell and Iriver.
In a statement a Microsoft spokesperson said: "Since Zune is a separate offering that is not part of the Plays For Sure ecosystem, Zune content is not supported on Plays For Sure devices."
The spokesperson continued: "We will not be performing compatibility testing for non-Zune devices, and we will not make changes to our software to ensure compatibility with non-Zune devices."
The changes to MSN Music do not mean that users will no longer be able to listen to the music they have bought via the store. Users will be able to burn files to a CD for their own use or put them on "compatible players".
Microsoft said that its Windows Media Player will recognise Zune content which might make it possible to put the content on a Plays For Sure device. However, it said it would not provide customer support to anyone attempting this.
'In a bind'
When Microsoft launched the MSN Music store in 2004, it hoped to compete with Apple.
But the service failed to make a dent in Apple's huge share of the online music market, and the company has now turned to a different tactic.
Microsoft's strategy for Zune replicates that of Apple's iPod - to control both the device and music service.
From 14 November, customers on the MSN Music store site will now be redirected to Zune Marketplace or, as part of a 2005 legal settlement where Microsoft agreed that no music service would receive greater promotion than RealNetworks, Real Rhapsody.
MSN Music store, the company said, would now be used for hosting live concerts, interviews with bands, and other music related-content.
In addition to causing problems for existing MSN-customers hoping to transfer files to the Zune player, the move could also leave users and manufacturers of other Plays For Sure compatible devices out in the cold.
The changes could hit owners of many MP3 players
In his blog, Jupiter Research technology analyst Michael Gartenberg said: "While it's not like there's a lot of folks that actually bought music from the MSN music store, it would seem those folks are in a bind.
"If they start buying from Zune, they will need to get to get a new Zune device, and their existing music won't go with them.
"If they go to Rhapsody, new stuff they purchase likely won't work on devices they currently own either, but at least a new Rhapsody compatible device will also allow them to play their old content."
"I'm surprised Microsoft didn't try to offer something like replacement for existing content in either Rhapsody or Zune formats."
Users of the Zune marketplace will be able to buy tracks individually or download unlimited tracks using a subscription fee.
Microsoft hopes the player's features, such as the ability to share music over wi-fi, will be its unique selling point.
The software giant said it would commit millions of dollars to making Zune a success but acknowledged it could take a long time for that success to become apparent.