Private Sub DataGridView1_Validated(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles DataGridView1.Validated
For i As Integer = 0 To DataGridView1.Rows.Count - 1
For j As Integer = i + 1 To DataGridView1.Rows.Count - 1
If DataGridView1.Rows(i).Cells(1).Value = DataGridView1.Rows(j).Cells(1).Value Then
MsgBox("Duplicate: " & DataGridView1.Rows(j).Cells(1).Value)
i think it will give you a "duplicate" message if column cardNumber has same value. try it
I Developed application in C# with crystal reports and created setup file in third party (Advance) Installer.When i installed my application on client system application is working but ...