The current type, is an interface and cannot be constructed. Are you missing a type mapping?

You might have missed to register your Interface and class (which implements that inteface) registration in your code.

e.g if the error is
"The current type, xyznamespace. Imyinterfacename, is an interface and cannot be constructed. Are you missing a type mapping?"

Then you must register the class which implements the Imyinterfacename in the UnityConfig class in the Register method. Using the following code as an example

using System;
using Microsoft.Practices.Unity;
using Microsoft.Practices.Unity.Configuration;
using PSC.Shorturl.Web.Business;
using PSC.Shorturl.Web.Business.Implementations;

namespace PSC.Shorturl.Web.App_Start
{
    /// 

    /// Specifies the Unity configuration for the main container.
    /// 
    public class UnityConfig
    {
        #region Unity Container
        private static Lazy container = new Lazy(() =>
        {
            var container = new UnityContainer();
            RegisterTypes(container);
            return container;
        });

        /// 

        /// Gets the configured Unity container.
        /// 
        public static IUnityContainer GetConfiguredContainer()
        {
            return container.Value;
        }
        #endregion

        /// 
Registers the type mappings with the Unity container.
        /// The unity container to configure.
        /// There is no need to register concrete types such as controllers or API controllers (unless you want to 
        /// change the defaults), as Unity allows resolving a concrete type even if it was not previously registered.
        public static void RegisterTypes(IUnityContainer container)
        {
            // NOTE: To load from web.config uncomment the line below. Make sure to add a Microsoft.Practices.Unity.Configuration to the using statements.
            // container.LoadConfiguration();

            // TODO: Register your types here
            container.RegisterType();
        }
    }
}