Несоотвествие типов данных в запросе - VB

Private Sub Command1_Click()
 Dim cmd, sql As String
    cmd = "Provider=microsoft.jet.OLEDB.4.0;" & "Data Source=" & App.Path & "\balance.mdb"
    Set cn = New ADODB.Connection
        With cn
            .ConnectionString = cmd
            .Open
        End With
         sql = "select nmrah, opis from spravrah where nmrah = '*" & a & "*' and opis = '*" & b & "*'"
         Set rs = New ADODB.Recordset
                With rs
                .ActiveConnection = cn
                .Source = sql
                .Open sql, cn, adOpenKeyset, adLockOptimistic
            End With
            rs("nmrah") = Text1.Text
            rs("opis") = Text2.Text
            rs.Update
            Flex1.Refresh
             Set rs = Nothing
   cn.Close
   Set cn = Nothing
End Sub