Cannot implicitly convert type 'System.Collections.Generic.IEnumerable<System.Web.Mvc.SelectListItem>' to 'System.Collections.Generic.IEnumerable

Hello Experts,

I'm totally new to programming using MVC in .net 4.5 and using (DB first) approach beside scaffolding way to create controllers and views from existing models.

When I rum my application I got those 2 errrors:

1- Cannot implicitly convert type 'System.Collections.Generic.IEnumerable<System.Web.Mvc.SelectListItem>' to 'System.Collections.Generic.IEnumerable<WebApplication2.Models.tb_List_AgencyCategory>'. An explicit conversion exists (are you missing a cast?)

2-'IEnumerable<tb_List_AgencyCategory>' does not contain a definition for 'Concat' and the best extension method overload 'Queryable.Concat<SelectListItem>(IQueryable<SelectListItem>, IEnumerable<SelectListItem>)' requires a receiver of type 'IQueryable<SelectListItem>'


Here is my Model Code:

namespace WebApplication2.Models
{
    using System;
    using System.Collections.Generic;
    using System.ComponentModel.DataAnnotations;
    using System.Linq;
    using System.Web.Mvc;
    using System.Collections;
    
    
    public partial class tb_Current_Agency
    {
        [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Usage", "CA2214:DoNotCallOverridableMethodsInConstructors")]
        public tb_Current_Agency()
        {
            this.tb_Current_Activation = new HashSet<tb_Current_Activation>();
            this.tb_Current_Activation1 = new HashSet<tb_Current_Activation>();
            this.tb_Current_GSBService = new HashSet<tb_Current_GSBService>();
            this.tb_List_AgencyCategory = new HashSet<tb_List_AgencyCategory>();
        }

        public string AgencyID { get; set; }
        public string AgencyArabicName { get; set; }
        public string AgencyEnglishName { get; set; }
        public string AgencyEnglishNameAbbreviation { get; set; }
        public Nullable<int> AgencyCategoryID { get; set; }

        [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Usage", "CA2227:CollectionPropertiesShouldBeReadOnly")]
        public virtual ICollection<tb_Current_Activation> tb_Current_Activation { get; set; }
        [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Usage", "CA2227:CollectionPropertiesShouldBeReadOnly")]
        public virtual ICollection<tb_Current_Activation> tb_Current_Activation1 { get; set; }
        public virtual tb_Current_Consumer tb_Current_Consumer { get; set; }
        [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Usage", "CA2227:CollectionPropertiesShouldBeReadOnly")]
        public virtual ICollection<tb_Current_GSBService> tb_Current_GSBService { get; set; }
        public virtual tb_Current_Provider tb_Current_Provider { get; set; }
        [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Usage", "CA2227:CollectionPropertiesShouldBeReadOnly")]
        public virtual ICollection<tb_List_AgencyCategory> tb_List_AgencyCategory { get; set; }
        //public int SelectedAgencyCategoryID { get; set; }

        public class AgencyCategory
        {
            public int AgencyCategoryID { get; set; }
            public string AgencyCategoryName { get; set; }
        }

         
        public readonly List<AgencyCategory> _Categories;

        [Display(Name = "Favorite Category")]
        public int SelectedAgencyCategoryID { get; set; }

        public IEnumerable<tb_List_AgencyCategory> CategoryItems
        {
            get
            {
                var allCategories = _Categories.Select(f => new SelectListItem
                {
                    Value = f.AgencyCategoryID.ToString(),
                    Text = f.AgencyCategoryName
                }).ToList();
                return DefaultCategoryItem.Concat(allCategories);
            }
        }

        public IEnumerable<tb_List_AgencyCategory> DefaultCategoryItem
        {
            get
            {
                return Enumerable.Repeat(new SelectListItem
                 {
                    Value = "-1",
                    Text = "Select a flavor"
                }, count: 1);
            }
        }
     


    }
}

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my View code:

 
@model PagedList.IPagedList<WebApplication2.Models.tb_Current_Agency>
@using PagedList.Mvc;
@using System.Linq;
@using WebApplication2.Models;

@{
    ViewBag.Title = "Index";
}

<h2>tb_Current_Agency</h2>

<p>
    @Html.ActionLink("Create New", "Create")
</p>

<Div class="active">

    <p>
        @using (Html.BeginForm("Index", "tb_Current_Agency", FormMethod.Get))
        {
            <b>Search by:</b>
            @Html.RadioButton("searchBy", "AgencyID")<text> AgencyID</text>
            @Html.RadioButton("searchBy", "AgencyArabicName")<text>AgencyArabicName</text>
            <br />
            @Html.RadioButton("searchBy", "AgencyCategoryID")<text>AgencyCategoryID</text>
            <br />
            @Html.TextBox("Search");
            <input type="submit" value="Search" />
        }

       
    </p>       
        </Div>
    

    <table class="table">
        <tr>
            <th>

                @Html.DisplayNameFor(model => model.First().AgencyID)
            </th>
            <th>
                @Html.DisplayNameFor(model => model.First().AgencyEnglishName)
            </th>
            <th>
                @Html.DisplayNameFor(model => model.First().AgencyEnglishNameAbbreviation)
            </th>
            <th>
                @Html.DisplayNameFor(model => model.First().AgencyCategoryID)
            </th>
            <th>
            @*@Html.LabelFor(m => m.First().SelectedAgencyCategoryID)*@
                @*@Html.DropDownListFor(m => m.SelectedFlavorId, Model.FlavorItems)*@
            @Html.DropDownListFor(m => m.First().AgencyCategoryID, Model.First().CategoryItems)
            @*@Html.ValidationMessageFor(m => m.First().SelectedAgencyCategoryID)*@


           </th>
        </tr>

        @foreach (var item in Model)
        {
            <tr>

                <td>
                    @Html.DisplayFor(modelItem => item.AgencyID)
                </td>
                <td>
                    @Html.DisplayFor(modelItem => item.AgencyArabicName)
                </td>
                <td>
                    @Html.DisplayFor(modelItem => item.AgencyEnglishName)
                </td>
                <td>
                    @Html.DisplayFor(modelItem => item.AgencyEnglishNameAbbreviation)
                </td>
                <td>
                    @Html.DisplayFor(modelItem => item.AgencyCategoryID)
                </td>
                
                <td>
                    @Html.ActionLink("Edit", "Edit", new { id = item.AgencyID }) |
                    @Html.ActionLink("Details", "Details", new { id = item.AgencyID }) |
                    @Html.ActionLink("Delete", "Delete", new { id = item.AgencyID })
                </td>
            </tr>
        }

       

        <tr>

          
            @Html.PagedListPager(Model, page => Url.Action("Index", new { page, searchBy = Request.QueryString["searchBy"], search = Request.QueryString["search"] }), new PagedListRenderOptions() { Display = PagedListDisplayMode.IfNeeded, DisplayItemSliceAndTotal = true })


        </tr>

    </table>

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Please tell me how to fix this error.



Thanks a lot in advance.
Harreni