UPDATE (16 AUG): We fixed the digital certificate problem and last evening resumed publishing new apps and updates. It will take a day or two for the repair to fully deploy and newly-published apps to begin appearing in Marketplace again. If you experienced errors, I want to emphasize that you don’t need to do anything to start downloading new apps or updates once the repair has finished rolling out.
If you’ve tried to download or update an app this week and keep getting an error message, I want to briefly explain why and what we’re doing about it.
What’s going on
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.
What we’re doing
We know what’s causing the issue and are already planning to roll out a fix. Until that’s finished, we’re going to temporarily stop publishing new apps in Marketplace.
If you get an error message while installing or updating an app, the best thing to do is wait for us to correct the problem, which we’re working to do as quickly as possible. 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. Also, you’d lose any saved data for that app. Again, the vast majority of apps and games in Marketplace should install without trouble.
I’ll update you when there’s more news.