Microsoft is in the midst of what it says is a major backend overhaul to the infrastructure for the Windows Phone Store (neé Windows Phone Marketplace). Apparently there have been some bumps in the road — specifically many users have been unable to download or update apps. The error, according to a blog post at Microsoft's Windows Phone Blog, is related to digital certificates and should only affect users who have upgraded their phones to version 7.5, while those who had that version of the OS preinstalled should be ok. Microsoft says it's working on a fix now, but in the meantime the company is not going to publish new Windows Phone apps to the store.
"Please ignore this message. We are working to resolve this issue as quickly as we can, please take no further action until the issue is resolved."
Until Microsoft fixes the bug, users who are running into these problems will just need to deal with the errors. In another posting, Microsoft is recommending users "ignore" the error messages for the time being. Unfortunately, uninstalling any of the affected apps will likely mean that you won't be able to re-install them until Microsoft quashes the bug, and from the company's various postings it doesn't appear as though there's a way to get around that issue right now. Microsoft hasn't given an ETA for when it will fix up the Store, though it does say that "We know what’s causing the issue and are already planning to roll out a fix."
Update: Microsoft has resolved the issue and resumed app publishing, providing a statement in the Windows Phone Blog:
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.