c# - Enum as a parameter in a method, looping through the enum produces invalid cast

This is what I have:

    private IEnumerable GetAllEnumValues(Enum enumValues)
    {
        var allEnumValues = new List();
        var values = Enum.GetValues(enumValues.GetType());
        foreach (var selectedItem in values)
        {
            allEnumValues.Add(new SelectListItem
                                  {

                                      Value = ((int)selectedItem).ToString(),
                                      Text = selectedItem.ToString()
                                  });
        }

        return allEnumValues.AsEnumerable();
    }

This is how the method is called:

AllAgencies = GetAllEnumValues((AgencyCodes) 0)

Build is fine, but when the method is actually used, I get "Specified cast is not valid." yellow screen of death on the .Add line. I need the Value of the SelectListItem to be the actual enum number, just casted to string. So far I tried all of these:
C# Iterating through an enum? (Indexing a System.Array), Enum in C# and foreach, How do I enumerate an enum? and in the end I always end up with the same error. I'm using .NET 4.0.

Answer

That usually means that your enum is not based on int, for example:

enum AgencyCodes : short {

    ...
}

You can't unbox an enum to the wrong type of value.