ERROR: Cannot find all types required by the 'async' modifier. Are you targeting the wrong framework version, or missing a reference to an assembly?

Question

I have following configuration of my PC:

• Windows 8
• Visual Studio 2012
• .NET Framework 4.5

My Project Configuration is:

Answer 1

From the page you downloaded from:

This targeting pack is not required for projects targeting .NET Framework 4.5 or .NET for Windows Store apps. It is only required for projects targeting Silverlight 5 and .NET Framework 4.0. Earlier platform releases are not supported.

Upgarde to Silverlight 5?