Are you a Windows Phone 8 developer using Visual Studio 2012 and have you downloaded and upgraded your Windows 8 machine to Windows 8.1 Preview?.

When trying to run the Windows Phone 8 emulator from Visual Studio 2012 , you might notice an issue which restricts you to run the Emulator because of the compatibility issues from Visual Studio 2012 as shown in the below screenshot.

 In order to resolve this issue, you will need to install the Microsoft Visual Studio 2012 Update 3 on your system. This will fix the issue.

You can download the Microsoft Visual Studio 2012 Update 3 from Microsoft Download Center

See Also

Another important place to find a huge amount of Windows Phone related articles is the TechNet Wiki itself. The best entry point is Windows Phone Resources on the TechNet Wiki.