Zune users in the US who were waiting for an important firmware update from Microsoft were disappointed on Tuesday when the company didn't deliver on schedule.

Microsoft had said it would release an update on 20 March that would correct a problem that caused songs purchased on the Zune Marketplace to skip when users would first play them, according to the Bink.nu blog. Users also reported having problems synching their Zunes with their PCs and were hoping the update will correct this, too.

Cesar Menendez, a member of the Zune marketing team at Microsoft who writes the Zune Insider blog, reported yesterday that the Zune engineering team was still working on the update but does not have a specific date for when it will be released.

"So there, you have it, dear blog reader," he wrote, after posting the information he received from Microsoft employees responsible for Zune firmware. The update will be available "soon”.

Blog readers who were expecting the update met the news with a host of frustrated responses. They can be viewed on the Zune Insider blog.

Microsoft released Zune and the Zune Marketplace in the US November 2006 to compete with Apple's iPod devices and iTunes online music service. The product is due to launch in the UK later this year.

So far, analysts have reported that Zune has not substantially affected iPod market share.