I have problem with Visual Studio 2012 (OS: Windows 8.1 Preview)
Windows 8.1 Preview
does not support the Windows Phone 8 sdk
to run on the Visual Studio 2012
. You cannot run Emulator as well so better you should use a stable Windows 8 version
for WP8
development. This is the statement right from Microsoft Support
After you upgrade your OS to Windows 8.1 Preview, you cannot run Windows Phone 8 Software Development Kit (SDK) emulator (XDE.exe) in Microsoft Visual Studio 2012
Reference here