Hello guys It worked finally with the following code:
Private Sub cmbmain_SelectedValueChanged(sender As Object, e As EventArgs) Handles cmbmain.SelectedValueChanged
lstitem.Items.Clear()
Con.Open()
Dim cmd As New OleDbCommand("select * from items where cat_name='" & cmbmain.Text & "'", Con)
Dim dr As OleDbDataReader = cmd.ExecuteReader
While dr.Read
lstitem.Items.Add(dr(1).ToString.ToUpper)
End While
dr.Close()
Con.Close()
End Sub
I thank Mt Maciej Los for his kind help.
Thank you