Access IRegionManager Object from a Module ViewModel - Prism with Unity

Question

I am trying to access the regionManager of the Shell from the Viewmodel of a module in a WPF-Prism Application with Unity for view-based Navigation

Following is the constructor of the ViewModel for a Module.

public LeftSelectionViewModel(IRegionManager regionManager)
{
     _regionManager = regionManager;                
}

Seems can't construct the Viewmodel object(I use auto-wiring).

Works fine when I remove the parameter from the Constructor.

What is missing?