Microsoft scramble to fix problem preventing users from downloading apps to handsets.
Microsoft has stopped the publication of new apps for Windows Phones following an issue with digital security certificates.
At the moment it seems only affect users who have updated their handsets to Windows Phone 7.5 - those who have purchased their phone with 7.5 pre-installed are fine.
Mazhar Mohammed, director of program management at Microsoft wrote: "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."
Microsoft is currently in the process of rebranding the Windows Phone Marketplace.