Visual Basic.NET - Problemas con ADDHANDLER

Al momento que se produce un error en el metodo FILL del dataadapter por ejm,por que un cursor de oracle no se inicializo(manejador de sentencias no ejecutado) no se reconoce el evento FILLERROR y no entra al prcedimiento asociado(DataAdapterOnFillError). Muchas Gracias

Private Sub Button4_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button4.Click
Dim db As New BaseDatos
Try
db.Conectar()
db.CrearComando("aa", CommandType.StoredProcedure)
db.AsignarParametro("cur_unidad", OracleType.Cursor)
db.AsignarParametro("cur_err", OracleType.Cursor)
db.Desconectar()
Dim ds As DataSet = db.EjecutarDataSet
grid3.DataSource = ds.Tables(0).DefaultView
Catch ex As Excepcion
MessageBox.Show(ex.Excepcion)
End Try
End Sub

Public Function EjecutarDataSet() As DataSet
Try
Dim da As OracleDataAdapter = objFactory.CreateDataAdapter

da = New OracleDataAdapter
AddHandler da.FillError, AddressOf DataAdapterOnFillError
da = objFactory.CreateDataAdapter

Dim ds As DataSet = New DataSet
da.SelectCommand = ObjComando

Dim r As New DataSet
da.Fill(r)
'RemoveHandler da.FillError, AddressOf DataAdapterOnFillError

Me.ObjComando.Parameters.Clear()
Return ds
Catch ex As Exception
Throw New Excepcion("Error originado por EjecutarDataset", ex)
End Try
End Function

Public Sub DataAdapterOnFillError(ByVal sender As Object, ByVal e As System.Data.FillErrorEventArgs)
MsgBox("hola")
e.Continue = True
End Sub