ASP.NET

public class ElmahLog : Elmah.ErrorLog
{
    public override string Log(Error error)
    {

        throw new System.NotImplementedException();

    }

    public override ErrorLogEntry GetError(string id)
    {

        throw new System.NotImplementedException();

    }

    public override int GetErrors(int pageIndex, int pageSize, IList errorEntryList)
    {

        throw new System.NotImplementedException();

    }
}

Protected Sub Grid1CheckChanged(ByVal sender As Object, ByVal e As EventArgs)
     'Dim hasBlank As Boolean = False
     For Each row As GridViewRow In Gridview1.Rows
         Dim ename As TextBox = TryCast(row.FindControl("txtsourcename"), TextBox)
         Dim empaddress As TextBox = TryCast(row.FindControl("txtsourceaddress"), TextBox)
         Dim empincomesrc As TextBox = TryCast(row.FindControl("txtsourceincome"), TextBox)
         Dim sourceCheck As CheckBox = DirectCast(Gridview1.FindControl("grid1Details"), CheckBox)
         If Not sourceCheck.Checked Then
             'hasBlank = True
             ename.Enabled = True
             empaddress.Enabled = True
             empincomesrc.Enabled = True
         ElseIf Not sourceCheck.Checked And ename.Text Is Nothing And empaddress.Text Is Nothing And empincomesrc.Text Is Nothing Then
             lblStatus.Text = "Please either fill out the textboxes or check the checkbox."
         Else
             ename.Enabled = False
             empaddress.Enabled = False
             empincomesrc.Enabled = False
         End If
     Next
 End Sub

<script type="text/javascript">

    function ValidateTextBox() {
        checkbox = document.getElementById("grid1Details");
        var textvalue = $(".textClass").attr('value');
        if (!checkbox.checked &&  textvalue != "") {
                alert("Either check the box or enter value in all textboxes.");
                return false;
            }
            return true;
        }

</script>

<td> <asp:Button ID="btnNext" CssClass="btnNext" runat="server" Text="Review Form" OnClientClick="BtnClick();javascript:return ValidateTextBox();" OnClick="btnNext_Click" /></td>

   <table>
    <tr>
        <td>
          <asp:gridview ID="Gridview1" gridlines="None" runat="server" ShowFooter="true" AutoGenerateColumns="false" OnRowDeleting="Gridview1_RowDeleting">
            <Columns>
            <asp:BoundField DataField="RowNumber" Visible="false" HeaderText="Row Number" />
            <asp:TemplateField HeaderText="Name">
             <headerstyle horizontalalign="Left" />
                <ItemTemplate>
                    <asp:TextBox ID="txtsourcename" CssClass="textClass" placeholder="Name...(e.g, Jane Doe)" runat="server" style="width:250px;" class="form-control"></asp:TextBox><br />
                    <asp:CheckBox ID="grid1Details" ClientIDMode="Static" runat="server" Checked="false" AutoPostBack="true" OnCheckedChanged="Grid1CheckChanged" /><span style="color:#ff0000">*Check this box if N/A</span>
                </ItemTemplate>
            </asp:TemplateField>
            <asp:TemplateField HeaderText="Address">
            <ItemStyle HorizontalAlign="Left"></ItemStyle>
                <ItemTemplate>
                    <asp:TextBox ID="txtsourceaddress" CssClass="textClass" placeholder="Address..." runat="server" style="width:250px;" class="form-control"></asp:TextBox><br /><br />
                </ItemTemplate>
            </asp:TemplateField>
            <asp:TemplateField HeaderText="Income">
            <ItemStyle HorizontalAlign="Left"></ItemStyle>
                <ItemTemplate>
                     <asp:TextBox ID="txtsourceincome" CssClass="textClass" placeholder="Income...(example: 1000)" runat="server" style="width:250px;" class="form-control txtsourceincome numeric"></asp:TextBox><br /><br />
                </ItemTemplate>
                       </asp:TemplateField>
            <asp:TemplateField HeaderText="">
                <ItemTemplate>
                 <asp:Button ID="ButtonAdd" runat="server" Text="Add" 
                        onclick="ButtonAdd_Click" CssClass="grvAddButton" OnClientClick="return ValidateEmptyValue();return validate()" /><br /><br /><br>
                </ItemTemplate>
            </asp:TemplateField>
            <asp:TemplateField HeaderText="">
                <ItemTemplate>
                 <asp:Button ID="sourceDelete" runat="server" Text="Delete" CommandName="Delete"
                         CssClass="grvDelButton" OnClientClick="return confirm('are you sure?')"  /> <br /><br /><br />
                </ItemTemplate>
            </asp:TemplateField> 
            </Columns>
          </asp:gridview>
        </td>
    </tr>
</table>

<pre><script type="text/javascript"> 
    window.onload = function scr1() {
        var div = document.getElementById("dvScroll");
        var div_position = document.getElementById("div_position");
        var position = parseInt('<%=!string.IsNullOrEmpty(Request.Form["div_position"]) ? Request.Form["div_position"] : "0" %>');
            div.scrollTop = position;
            div.onscroll = function () {
                document.getElementById("div_position").value = div.scrollTop;
            };
    };
</script>

<pre> <form id="form1" runat="server">
        <div id="dvScroll"; style="width:450px; height:300px; overflow:scroll; float:left">
            <asp:HiddenField ID="HiddenField1" runat="server" />
            <asp:GridView ID="GridView1" runat="server" AutoGenerateColumns="false" OnRowDataBound="GridView1_RowDataBound" OnRowCreated="GridView1_RowCreated" OnSelectedIndexChanged="GridView1_SelectedIndexChanged" CellPadding="4">
              <Columns>         
                <asp:BoundField DataField="ID_NAVE" HeaderText="IdNave" ItemStyle-Width="50" ItemStyle-wrap="false" Visible="true" />
                ....
              </Columns>
            </asp:GridView>
        </div>
        <input type="hidden" id="div_position" name="div_position" />

<pre><form id="form1" runat="server">
        <div id="dvScroll"; style="width:450px; height:300px; overflow:scroll; float:left">
            <asp:HiddenField ID="HiddenField1" runat="server" />
            <asp:GridView ID="GridView1" runat="server" AutoGenerateColumns="false" OnRowDataBound="GridView1_RowDataBound" OnRowCreated="GridView1_RowCreated" OnSelectedIndexChanged="GridView1_SelectedIndexChanged" CellPadding="4">
              <Columns>         
                <asp:BoundField DataField="ID_NAVE" HeaderText="IdNave" ItemStyle-Width="50" ItemStyle-wrap="false" Visible="true" />
                ....
              </Columns>
            </asp:GridView>
        </div>
        <input type="hidden" id="div_position" name="div_position" />

       <div id="dvScroll2"; style="clear:both; width:600px; height:300px; overflow:scroll;">       
           <asp:HiddenField ID="HiddenField2" runat="server" />
           <asp:GridView ID="GridMnuRest" runat="server" AutoGenerateColumns="false" CellPadding="4" OnRowCreated="GridMnuRest_RowCreated" OnRowDataBound="GridMnuRest_RowDataBound" OnSelectedIndexChanged="GridMnuRest_SelectedIndexChanged" OnSelectedIndexChanging="GridMnuRest_SelectedIndexChanging" OnRowCommand="GridMnuRest_RowCommand">                            
               <Columns>       
                <asp:TemplateField >
                  <ItemTemplate>
                    <asp:CheckBox ID="MnuSelect" runat="server" AutoPostBack="true" OnCheckedChanged="GridMnuRest_OnCheckedChanged" />
                  </ItemTemplate>
                </asp:TemplateField>                  
               <asp:BoundField DataField="id_ristorante" HeaderText="IdRst" ItemStyle-Width="20" ItemStyle-wrap="false" Visible="true" />
              </Columns>
           </asp:GridView>
       </div>
       <input type="hidden" id="div_position2" name="div_position2" />
    </form>

<?xml version=\"1.0\"?>\n<definitions xmlns=\"http://schemas.xmlsoap.org/wsdl/\" xmlns:tns=\"http://xxx.xx.xxx.xxx/ws/servicexx/xx/web/xxxx/index?ws=1\" xmlns:soap=\"http://schemas.xmlsoap.org/wsdl/soap/\" xmlns:xsd=\"http://www.w3.org/2001/XMLSchema\" xmlns:soap-enc=\"http://schemas.xmlsoap.org/soap/encoding/\" xmlns:wsdl=\"http://schemas.xmlsoap.org/wsdl/\" name=\"xx.xxx.xx.xxcontrollers.xxxxController\" [...]

How to fix error "the type or namespace name 'CustomerBAL' could not be found (are you missing a using directive or an assembly reference) 

Name project MvcApplication1) on ASP.Net Visual Studio 2012 
Could anyone help me ? Thank's in advance ...

public class Book
    {
        [Key]
        public int Id { get; set; }
        [Required]
        [MaxLength(30)]
        public string Title { get; set; }
        public string Authers { get; set; }
 
        [Column("Year")]
        [Display(Name = "Publish Year")]
        public string publishYear { get; set; }
 
        [Column("Price")]
        [Display(Name = "Price")]
        public decimal BasePrice { get; set; }
    }

public interface IBookRepository : IDisposable
        {
            IEnumerable<Book> GetBooks();
            Book GetBookByID(int bookId);
            void InsertBook(Book book);
            void DeleteBook(int bookID);
            void UpdateBook(Book book);
            void Save();
    }

public class BookRepository : IBookRepository
    {
        private BookContext _context;
 
        public BookRepository(BookContext bookContext)
        {
            this._context = bookContext;
        }
 
        public IEnumerable<book> GetBooks()
        {
            return _context.Books.ToList();
        }
 
        public Book GetBookByID(int id)
        {
            return _context.Books.Find(id);
        }
 
        public void InsertBook(Book book)
        {
            _context.Books.Add(book);
        }
 
        public void DeleteBook(int bookID)
        {
            Book book = _context.Books.Find(bookID);
            _context.Books.Remove(book);
        }
 
        public void UpdateBook(Book book)
        {
            _context.Entry(book).State = EntityState.Modified;
        }
 
        public void Save()
        {
            _context.SaveChanges();
        }
 
        private bool disposed = false;
 
        protected virtual void Dispose(bool disposing)
        {
            if (!this.disposed)
            {
                if (disposing)
                {
                    _context.Dispose();
                }
            }
            this.disposed = true;
        }
 
        public void Dispose()
        {
            Dispose(true);
            GC.SuppressFinalize(this);
        }
    }