see with one more condition
@if(ViewBag.EmployeeTypeName !=null){
@Html.DropDownListFor(m => m.EmployeeType.Name,(IEnumerable<SelectListItem>)ViewBag.EmployeeTypeName, "select city")
}
make a to use ToList() for viewbag object because it needs enumerable list
ViewBag.EmployeeTypeName = new SelectList(employee.EmployeeType.ToList(), "EmployeeTypeID", "Name", "EmployeeTypeID");
;