Strange NullReferenceException on ExecuteReader

when I try to execute the folowing code, a NullReferenceException is raised on the ExecuteReader:

static public IDataReader executeReader(string query, string connectionString, string databaseType)
    {
        switch(databaseType)
        {               
            case "SqlServer":
                //stuff for Sql Server      
            case "DB2":
                iDB2Connection myConnectionDB2 = new iDB2Connection(connectionString);

                iDB2Command sqlCommandDB2 = new iDB2Command(query,  myConnectionDB2);
                sqlCommandDB2.CommandTimeout=0;
                try
                {                       
                    sqlCommandDB2.Connection.Open();
***The exception is raised here...***
                    return sqlCommandDB2.ExecuteReader(CommandBehavior.CloseConnection);
                }
                catch (Exception e)
                {
                    sqlCommandDB2.Dispose();
                    myConnectionDB2.Close();
                    throw new Exception("Error in DBHelper:ExeSQL()-> " + e.ToString());
                }       
            default:
                //stuff for Oracle
        }                           
    }

Here is the message exception:

System.NullReferenceException: La référence d'objet n'est pas définie à une instance d'un objet. at Microsoft.Win32.Win3开发者_如何转开发2Native.CopyMemoryUni(StringBuilder pdst, IntPtr psrc, IntPtr sizetcb) at System.Runtime.InteropServices.Marshal.PtrToStringUni(IntPtr ptr) at IBM.Data.DB2.iSeries.MPHostCol.setHostColInfo(MpDcHostColumnInfo dcHostColInfo) blahblahblah until the line above.

Every parameter is filled, the query execute correctly with SQL-view, the connection string is correct and the database type is ok... As every static method, nothing else have to be set... i'm sure it's somethin' stupid, but can't figure what.

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Damn, the update from V5R3 to V5R4 has solved the bug. A simple 15 minutes update solved 3 days of head banging. Glad to have contributed :)