ODP.NET

Hallo

i have a query with two parameters. I get not result when I execute the query.

I do tests:
- Query works well in Oracle SQL Developer (with parameters)
- Same query works with System.Data.OracleClient
- Same query works with one of the parameters
- Another query with 2 parameters works correct (which does not contain the 'where not exists')

here is the statement:
OracleCommand command = new OracleCommand(
"select count(*) as anzahl_ds from bi_zas_zuordnung t1 where not exists (select cover_e_mandant, cover_obj_nr, cover_ausg, cover_jahr, cover_hnr from bi_zas_zuordnung t2 where t1.cover_e_mandant = t2.cover_e_mandant and t1.cover_obj_nr = t2.cover_obj_nr and t1.cover_ausg = t2.cover_ausg and t1.cover_hnr = t2.cover_hnr and t2.cover_jahr = :JAHR_NACH) and t1.cover_jahr = :JAHR_VON",connection);

command.Parameters.Add(new OracleParameter(":JAHR_VON", OracleDbType.Int32));
command.Parameters.Add(new OracleParameter(":JAHR_NACH", OracleDbType.Int32));
command.Parameters[0].Value = 2008;
command.Parameters[1].Value = 2043;

OracleDataReader dataReader = command.ExecuteReader();
while (dataReader.Read())
{
this.textBox1.Text = dataReader[0].ToString();
}

Any ideas where the error could be (I think it is the problem of the ODP.NET)

Regards
Gernot