Just playing with Xamarin.Forms, downloaded sample project TipCalc from here. When I try to open the solution in Xamarin Studio I am getting this error.

When i try to build the project, i get this error
Error MSB4019: The imported project "C:\Program Files (x86)\MSBuild\Microsoft\Portable\v4.5\Microsoft.Portable.CSharp.targets" was not found. Confirm that the path in the declaration is correct, and that the file exists on disk. (MSB4019) (TipCalc.Android)
Please someone guide me, what should i configure in my project, to make this to run successfully. I am using Xamarin Studio 5, my OS is windows 7 ultimate.