DATA READER Of SQL UNHANDLED - Choose One Record From Combo Box That Is Bind From Name

Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
Dim asm As String
asm = ComboBox2.Text
cmdOLEDB.CommandText = "SELECT * FROM sale "
cmdOLEDB.Connection = cnnOLEDB
Dim ab = DateTime.Now.ToString("MM/dd/yyyy HH:mm:ss")
Dim dr = cmdOLEDB.ExecuteReader

[CODE]...

I choose one record from combo box... that is bind from name after that when i select another it gives error