Unable to update a access database in asp.net

 Imports System.Data
Imports System.Data.OleDb
Public Class Customer_Details
    Inherits System.Web.UI.Page
    Dim sql As String
    Dim cmd As OleDbCommand
    Dim dr As OleDbDataReader
 
    Dim conn As OleDbConnection = New OleDbConnection(ConfigurationManager.ConnectionStrings("dbconnection").ConnectionString)
    Dim da As OleDbDataAdapter
    Dim dt As New DataTable
 
    Protected Sub btnback_Click(ByVal sender As Object, ByVal e As EventArgs) Handles btnback.Click
        Response.Redirect("Customer.aspx")
    End Sub
    Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
        Me.txtCustNo.Text = Request.QueryString("ID")
        load_Cust()         'Show data Basic Information of Textbox

        btnUpdate.Visible = False
        btnCancle.Visible = False
 
        'Menu Show / Hide
        pnAdmin.Visible = True
        pnUser.Visible = False
 
        Hhide_pan()
        ''
    End Sub
    Protected Sub Hhide_pan()
        pnAddContact.Visible = False
        pnAddMachine.Visible = False
    End Sub
    Public Function FixNull(ByVal o As Object) As Object
        If IsDBNull(o) Then
            Return Nothing
        Else
            Return o
        End If
    End Function
    Protected Sub load_Cust()   'Show data Basic Information of Textbox
        Try
            sql = "SELECT Firstname, Lastname, Company, Address, City, Pincode, State, Email, STD, Phoneno, Mobile, Customertype, Duration, Startdate, Enddate FROM tblCustomer WHERE CustomerID=" & txtCustNo.Text & ""
            conn.Open()
            cmd = New OleDbCommand(sql, conn)
            dr = cmd.ExecuteReader(CommandBehavior.CloseConnection)
            If dr.Read Then
                txtFirstName.Text = dr(0)
                txtLastName.Text = dr(1)
                txtCompany.Text = FixNull(dr(2))
                txtAddress.Text = dr(3)
                txtCity.Text = dr(4)
                txtPincode.Text = dr(5)
                txtState.Text = dr(6)
                txtEmail.Text = FixNull(dr(7))
                txtSTD.Text = dr(8)
                txtPhone.Text = dr(9)
                txtMobile.Text = dr(10)
                drpCustType.SelectedItem.Text = dr(11)
                If drpCustType.SelectedItem.Text = "AMC" Then
                    drpDuration.SelectedItem.Text = dr(12)
                    txtStartDate.Text = dr(13)
                    txtEndDate.Text = dr(14)
                End If
            End If
        Catch ex As Exception
            MsgBox(ex.Message)
        Finally
            cmd.Dispose()
            conn.Close()
        End Try
    End Sub
    Protected Sub Update_Customer()
        Try
            ''sql = "UPDATE tblCustomer SET [Firstname] = '" & txtFirstName.Text & "', [Lastname] = '" & txtLastName.Text & "', [Company] = '" & txtCompany.Text & "', [Address] = '" & txtAddress.Text & "', [City] = '" & txtCity.Text & "', [Pincode] = '" & txtPincode.Text & "', [State] = '" & txtState.Text & "', [Email] = '" & txtEmail.Text & "', [STD] = '" & txtSTD.Text & "', [Phoneno] = '" & txtPhone.Text & "', [Mobile] = '" & txtMobile.Text & "', [Customertype] = '" & drpCustType.SelectedItem.Text & "', [Duration] = '" & drpDuration.SelectedItem.Text & "', [Startdate] = '" & txtStartDate.Text & "', [Enddate] = '" & txtEndDate.Text & "' WHERE [CustomerID]=" & txtCustNo.Text & " "
            sql = "UPDATE tblCustomer SET Firstname = @FN, Lastname = @LN, Company= @CO, Address = @AD, City = @CI, Pincode = @PI, State = @ST, Email = @EM, STD = @STD, Phoneno = @PN, Mobile = @MN, Customertype = @CT, Duration = @DU, Startdate = @SD, Enddate = @ED WHERE CustomerID = @CID"
            conn.Open()
            Trace.Write(sql)
            cmd = New OleDbCommand(sql, conn)
            cmd.Parameters.AddWithValue("@FN", txtFirstName.Text)
            cmd.Parameters.AddWithValue("@LN", txtLastName.Text)
            cmd.Parameters.AddWithValue("@CO", txtCompany.Text)
            cmd.Parameters.AddWithValue("@AD", txtAddress.Text)
            cmd.Parameters.AddWithValue("@CI", txtCity.Text)
            cmd.Parameters.AddWithValue("@PI", txtPincode.Text)
            cmd.Parameters.AddWithValue("@ST", txtPincode.Text)
            cmd.Parameters.AddWithValue("@EM", txtEmail.Text)
            cmd.Parameters.AddWithValue("@STD", txtSTD.Text)
            cmd.Parameters.AddWithValue("@PN", txtPhone.Text)
            cmd.Parameters.AddWithValue("@MN", txtMobile.Text)
            cmd.Parameters.AddWithValue("@CT", drpCustType.SelectedItem.Text)
            cmd.Parameters.AddWithValue("@DU", drpDuration.SelectedItem.Text)
            cmd.Parameters.AddWithValue("@SD", txtStartDate.Text)
            cmd.Parameters.AddWithValue("@ED", txtEndDate.Text)
            cmd.Parameters.AddWithValue("@CID", txtCustNo.Text)
 
cmd.ExecuteNonQuery()
        Catch ex As Exception
            MsgBox(ex.Message)
        Finally
            cmd.Dispose()
            conn.Close()
        End Try
    End Sub
 
    Protected Sub btnedit_Click(ByVal sender As Object, ByVal e As EventArgs) Handles btnedit.Click
        btnUpdate.Visible = True
        btnCancle.Visible = True
    End Sub
 
    Protected Sub btnUpdate_Click(ByVal sender As Object, ByVal e As EventArgs) Handles btnUpdate.Click
        'Update_Customer()
        UpdateCust()
        Response.Redirect("Customer.aspx")
 
    End Sub
End Class