Feb 22, 2012 07:59 AM|Dino He - MSFT|LINK
You problem may because this issue:
WebPI V4 Alpha is installed as part of Visual Studio "11" and is intended to be upgraded to the Beta release immediately. If you open WebMatrix v1 before launching WebPI v4 Alpha, you will observe that the Application Gallery is empty.
Launch the Web Platform Installer from the Start menu and follow the prompts to complete the upgrade to WebPI v4 Beta. Then launch WebMatrix v1 again to successfully browse the Application Gallery.
Hope it helpful.