Microsoft is experiencing some problems with its Windows Phone Marketplace that are preventing users from downloading updates for their apps. The error, according to a blog post at Microsoft's Windows Phone Blog, is related to digital certificates and should only affect phones that upgraded to Windows Phone 7.5 from an earlier version. It does not appear to impact phones sold with Windows Phone 7.5 preinstalled.
Apparently, the problem hit during the rollout of the new Windows Phone Dev Center earlier this month. Only a small percentage of the 100,000-plus apps in Marketplace that have been updated recently are affected, including a few popular titles such as the New York Times, WhatsApp, and Translator from Bing.
Microsoft has identified the problem and is working on a fix. In the meantime, App publishing to the Windows Phone Marketplace has been put on hold. Curiously, those who have experienced problems updating apps will see an error message asking them to "uninstall the app then install it again" if the problem persists. However, Microsoft advises against it because it may be impossible to re-download the app until the fix is deployed.
It's worth noting that the momentary publishing freeze won't stop downloads of already-published apps.