Can not Upload More than 4mb file in ASP.net Application

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ASP.NET

I have a Asp.net application with file upload control in vb.net.In this application i can not upload more than 4 mb file.whenever i upload more than 4 mb it shows like Page Can not be Displayed Error

my Code is

Protected Sub btnUpload_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles btnUpload.Click

        Dim ValidAttachmentDescrption As Boolean
        lblErrormsg.Visible = False
        ValidAttachmentDescrption = ValidateDescription(txtAttachmentDescription.Text)

        If (ValidAttachmentDescrption = False) Then
            lblErrorMessage.Visible = True
            lblErrorMessage.Text = "Please enter the Description"
            mpeAttachment.Show()
        Else

            If (FileUploadControl.HasFile) Then
                Try
                    Dim ext As String = System.IO.Path.GetExtension(FileUploadControl.PostedFile.FileName)
                    Dim str As String = UploadExtension
                    Dim OriginalDate As String = Nothing
                    Dim OriginalTimestring As String = Nothing
                    Dim strs As String() = str.Split(","c)
                    Dim hfc As HttpFileCollection = Request.Files
                    For i As Integer = 0 To hfc.Count - 1
                        Dim hpf As HttpPostedFile = hfc(i)
                        If hpf.ContentLength > 0 Then
                            OriginalFilename = hpf.FileName
                            Dim tempFilename As String() = OriginalFilename.Split("."c)
                            Dim Fileextension As String = tempFilename(1)
                            Dim datestring As DateTime = DateTime.Now().ToShortDateString()
                            Dim timestring1 As String = DateTime.Now().ToShortTimeString()
                            Dim timestring2 As String() = timestring1.Split(":"c)
                            OriginalTimestring = String.Format("{0}{1}{2}", timestring2(0), timestring2(1), timestring2(2))
                            Dim datestring1 As String = datestring
                            Dim datestring2 As String() = datestring1.Split("/"c)
                            Dim minlength As Integer = datestring2(0).Length

                            If minlength = 1 Then
                                OriginalDate = String.Format("{0}0{1}{2}", datestring2(2), datestring2(0), datestring2(1))
                            Else
                                OriginalDate = String.Format("{0}{1}{2}", datestring2(2), datestring2(0), datestring2(1))
                            End If


                            FileName = String.Format("{0}_{1}{3}.{2}", ApplicationID, OriginalDate, Fileextension, OriginalTimestring)
                            ' _yyyyMMddhhmmss.<ext>.
                            'UploadExtension
                            Dim FiletypeArray As String() = UploadExtension.Split(","c)
                            Dim F1 As Integer = 0
                            Dim myArray As String() = New String(FiletypeArray.Count - 1) {}
                            For Each obj As String In FiletypeArray
                                Dim S1 As String = FiletypeArray(F1)
                                Dim S2 As String = String.Format(".{0}", S1)
                                F1 += 1
                                If obj <> Nothing Then
                                    If OriginalFilename.EndsWith(S2) Then
                                        ValidFiletype = True
                                    End If
                                End If

                            Next
                            If hpf.ContentLength > UploadSize Then
                                ValidFileLength = False
                            Else
                                ValidFileLength = True
                            End If
                            'If OriginalFilename <> "" And OriginalFilename.EndsWith(".jpg") Or OriginalFilename.EndsWith(".png") Or OriginalFilename.EndsWith(".pdf") Or OriginalFilename.EndsWith(".doc") Or OriginalFilename.EndsWith(".docx") Or OriginalFilename.EndsWith(".mp3") Then
                            If ValidFiletype = True AndAlso ValidFileLength = True Then
                                'hpf.SaveAs(Server.MapPath("~/UploadFiles") + System.IO.Path.GetFileName(hpf.FileName))
                                Dim filePath As String = _
         Server.MapPath("~/UploadFiles/" & FileUploadControl.FileName)
                                FileUploadControl.SaveAs(filePath)
                                CreateAttachment(ApplicationID, OriginalFilename, FileName, txtAttachmentDescription.Text)
                                SelectAttachment(ApplicationID)
                            Else
                                lblErrormsg.Visible = True
                                'lblErrormsg.Text = "File Extension is invalid"
                                lblErrormsg.Text = String.Format("File type error;we only accept{1}{0}", UploadExtension, WhiteSpace)
                            End If
                        Else

                        End If
                    Next

                Catch ex As Exception
                    Label1.Text = "ERROR: " & ex.Message.ToString()
                End Try
                'mpeAttachment.Hide()
                txtAttachmentDescription.Text = ""
                lblErrorMessage.Visible = False
            End If
        End If
    End Sub

Suggest me to solve this. Thanks in Advance