A Microsoft official said a problem with the site's security software was to blame. "We've run into an issue with the digital certificates used to sign apps, and this is preventing some phones from installing some apps published during the last couple of days," said Mazhar Mohammed, a Microsoft program director, in a blog post.
Mohammed did not say specifically what went wrong with the certificate system. Digital certificates allow senders and receivers of electronic messages and content to verify their identities, among other things.
Microsoft said the issue affected only "a small percentage" of the more than 100,000 apps in the Windows Phone Marketplace. Those affected include The New York Times app, WhatsApp, and Bing Translator.
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Further, only users with Windows Phone models that were updated from version 7 of the operating system to 7.5, also known as Mango, supposedly experienced the error.
"It does not appear to impact phones sold with Windows Phone 7.5 preinstalled," said Mohammed. "We know what's causing the issue and are already rolling out a fix. Until that’s finished we're going to temporarily stop publishing new apps in Marketplace."
Mohammed did not put a timeframe on Microsoft's efforts to fix the issue, but said the company is trying to resolve things "as quickly as possible." He also said Windows Phone users should leave their devices as is until the problem is fixed.
"I don't recommend uninstalling any apps on your phone, since you likely won't be able to download them again until the issue is resolved," Mohammed wrote. "Also, you'd lose any saved data for that app. Again, the vast majority of apps and games in Marketplace should install without trouble."
Customers seemed generally satisfied with Microsoft's response to the problem. "Thanks a lot for this (honest) information," wrote a user named Harald-Rene Flasch, in response to Mohammed's post.
Another, however, said his New York Times app was hit with the error even though his Windows phone, an HTC Titan X310e, came with Mango preinstalled. "After the update the app does not start," wrote user Bert Caris.
The problem isn't likely to put much of a dent in Windows Phone sales, unless it lingers. Microsoft is gearing up for the launch of Windows Phone 8, which is expected to arrive later this year.
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