Set ASP.Net DropDownList selected Text (Value) if found using VB.Net

Please help how can i undo the selected DropDownList value and set the DropDownList to a particular value in case of an error message

Using Com As New SqlCommand("Select * from Controlcream where stream = '" & streamr & "'", Con)
    Using RDR = Com.ExecuteReader()
        If RDR.HasRows Then
            Dim message As String = "alert('No Stream is Allowed to Cream Class.')"
            ScriptManager.RegisterClientScriptBlock(TryCast(sender, Control), Me.GetType(), "alert", message, True)
            dropDownList.ClearSelection()
            Dim item As Object = dropDownList.Items.FindByText(streamr)
            If item IsNot Nothing Then
                item.Selected = True
            End If 
Exit Sub