XLabs.Forms checkbox not working in iOS throwing exception

I Created Xamarin.Forms PCL project to work on CheckBox in Xamarin Studio(5.7) in Mac environment. I added XLabs.Forms package from Nuguet Package. CheckBox is working fine in android. But when i run the iOS it throws following exception: "Could not load file or assembly 'XLabs.Forms' or one of its dependencies. The system cannot find the file specified."
xmlns:controls="clr-namespace:XLabs.Forms.Controls;assembly=XLabs.Forms">

Please anyone give the solution