There's been a lot of positive things to say about the new Windows Phone Dev Center so far, but there's a nasty new glitch that may erase some of that praise for now. We noticed there was a lot of people complaining that they could not install updates to apps like New York Times or WhatsApp. and while we never experience this ourselves we knew there was something going on.
Speaking on the Windows Phone Blog and Windows Phone Developer Blog, Microsoft has addressed the issue and it is unfortunately due to a problem with the Dev Center. Here's Mazhar Mohammad's well-written explanation of what the problem is:
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.
We’ve investigated and determined the issue only affects phones that upgraded to Windows Phone 7.5 from an earlier version of the operating system. It does not appear to impact phones sold with Windows Phone 7.5 preinstalled.
We estimate the issue also affects only a small percentage of the 100,000-plus apps in Marketplace. Among the more popular ones affected are the New York Times, WhatsApp, and Translator from Bing—all of which recently issued new updates.
There’s nothing wrong with your phone and everything else should work fine.
The good news is that a fix is already underway, but will require some downtime. Therefore the Dev Center will be freezing app publishing until the fix is instated. It's also recommended that you do not uninstall the apps affected by this glitch as Todd Brix warns you, "might not be able to download and use [the affected apps] again until we deploy our fix". In other words, if there's a working version of the app on your phone, just hang on to it until we're in the clear.
Source: Windows Phone Blog, Windows Phone Developer Blog