¿que hago mal para que no me borre de la bd?

[beamm]

CUando hago esto no me da ningun error pero no me elimina de la bd. En la bd todos los kampos son string excepto el primero que sería la a que es integer.

Protected Sub aulasLibres_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles aulasLibres.Click
Dim a As Integer = DropDownList1.Text
Dim b As Char = DropDownList2.Text
Dim c As Char = DropDownList3.Text
Dim q As String = "DELETE FROM Reserva WHERE NumClase= @a and Fecha=@b and HoraInicio=@c"
Dim cnn As OleDbConnection



cnn = New OleDbConnection("Provider = Microsoft.Jet.OLEDB.4.0; Data Source = C:\Documents and Settings\Bea.BEA-095B12391FA\Mis documentos\Visual Studio 2005\WebSites\GestionAulas\App_Data\gestionaulas.m db")
Dim objCmd As New OleDbCommand(q, cnn)

objCmd.Parameters.Add(New OleDbParameter("@a", OleDbType.Integer))

objCmd.Parameters("@a").Value = a.ToString

objCmd.Parameters.Add(New OleDbParameter("@b", OleDbType.Char))
objCmd.Parameters("@b").Value = a.ToString
objCmd.Parameters.Add(New OleDbParameter("@c", OleDbType.Char))
objCmd.Parameters("@c").Value = a.ToString
objCmd.Connection.Open()

objCmd.ExecuteNonQuery()
objCmd.Connection.Close()

' Response.Redirect("~/Administrador.aspx")
End Sub