Object reference not set to an instance of an object.

Unhandled exception has occured in your application. if you click continue the application will ignores this error and attempt to continue if you click quit the application will close immediately.

Object reference not set to an instance of an object.

Imports System.Data.OleDb
Imports CrystalDecisions.CrystalReports.Engine
Imports CrystalDecisions.Shared
Public Class dbbillz

    Private Sub txtdisplaydetails_TextChanged(sender As Object, e As EventArgs) Handles txtdisplaydetails.TextChanged
        If txtdisplaydetails.Text = "Enter A Name" Then
            txtdisplaydetails.Text = ""
        End If
    End Sub
    Private Sub TextBox_Validate(sender As Object, e As EventArgs) Handles txtdisplaydetails.TextChanged
        If Not String.IsNullOrWhiteSpace(txtdisplaydetails.Text) Then btqmatesearch.Enabled = True
    End Sub

    Private Sub btqmatesearch_Click(sender As Object, e As EventArgs) Handles btqmatesearch.Click
        Dim rpt As New CrystalReport2
        Dim searchString As String
        searchString = txtdisplaydetails.Text.Trim().ToLower()
        estimatingbilldisplay.ReportSource = Nothing
        If (searchString.Equals("")) Then
            MessageBox.Show("Please enter some search string to print report.", "Empty value", MessageBoxButtons.OK, MessageBoxIcon.Warning)
            Return
        End If

        Dim DBCon As New OleDbConnection("Provider=Microsoft.ACE.OLEDB.12.0;" & _
                                     "Data Source=estimate.accdb;")
        estimatingbilldisplay.Enabled = True
        Dim tblDataEstimate As New DataTable
        Dim tblEstimateWk As New DataTable
        Dim tblClients As New DataTable

        Dim cmd As New OleDbCommand()
        cmd.Connection = DBCon
        Dim da As New OleDbDataAdapter(cmd)

        cmd.CommandText = "select * from tblClients where name='" + searchString + "'"
        da.Fill(tblClients)

        cmd.CommandText = "select * from tblDataEstimate where name='" + searchString + "'"
        da.Fill(tblDataEstimate)

        cmd.CommandText = "select * from tblEstimateWk where name='" + searchString + "'"
        da.Fill(tblEstimateWk)

        If (tblClients.Rows.Count = 0) Then
            MessageBox.Show("No records could be found matching your search criteria, please retry with possible matcing string", "No Records Found", MessageBoxButtons.OK, MessageBoxIcon.Information)
            Return
        End If
        rpt.Database.Tables("tblClients").SetDataSource(tblClients)
        rpt.Database.Tables("tblDataEstimate").SetDataSource(tblDataEstimate)
        rpt.Database.Tables("tblEstimateWk").SetDataSource(tblEstimateWk)
        estimatingbilldisplay.ReportSource = rpt
        estimatingbilldisplay.Refresh()
        estimatingbilldisplay.RefreshReport()
    End Sub

    Private Sub dbbillz_Load(sender As Object, e As EventArgs) Handles MyBase.Load
        If (Not IsApplicationActivated()) Then
            Me.Enabled = False
            Dim f = New frmActivation()
            f.ShowDialog()
            If (IsApplicationActivated()) Then
                Me.Enabled = True            
            End If
        End If
    End Sub

    Private Function IsApplicationActivated() As Boolean
        Try
            Dim Status = CryptoEngine.Decrypt(My.Settings.Activated.ToString(), SharedVars.salt)
            If (Convert.ToBoolean(Status)) Then
                Return True
            Else
                Return False
            End If
        Catch ex As Exception
            Return False
        End Try
    End Function
End Class

Public Class frmActivation

    Private Sub btnActivate_Click(sender As Object, e As EventArgs) Handles btnActivate.Click
        If (Not String.IsNullOrEmpty(Me.txtKey.Text.Trim())) Then
            Dim KeyCode As Long = -1
            KeyCode = Long.Parse(txtKey.Text.Trim())
            If (KeyCode <> -1) Then
                If (Security.CheckKey(KeyCode)) Then
                    lblStatus.BackColor = Color.White
                    lblStatus.ForeColor = Color.Green
                    lblStatus.Text = "Application Activated."
                    My.Settings.Activated = CryptoEngine.Encrypt("True", SharedVars.salt)
                    My.Settings.Save()
                    Me.Close()
                Else
                    lblStatus.BackColor = Color.White
                    lblStatus.ForeColor = Color.Red
                    lblStatus.Text = "Incorrect Activation Key, Please Try Again."
                End If
            Else
                lblStatus.Text = "Invalid Character Entered, Please Try Again."
            End If
        End If
    End Sub

    Private Sub btnCancel_Click(sender As Object, e As EventArgs) Handles btnCancel.Click

    End Sub

    Private Sub txtKey_KeyPress(sender As Object, e As KeyPressEventArgs) Handles txtKey.KeyPress
        If (Not Char.IsControl(e.KeyChar) And Not Char.IsDigit(e.KeyChar)) Then
            e.Handled = True
        End If
    End Sub

    Private Sub frmActivation_Load(sender As Object, e As EventArgs) Handles MyBase.Load
        Me.lblCode.Text += Environment.NewLine + Security.GetSerailNo().ToString()
    End Sub
End Class