how to export drawing to DXF

Hello again,
I have following method to export drawing to dxf but I have an exception pfcExceptions::XToolkitGeneralError on RetrieveModelWithOpts.
The export of part to 3dDXF from this thread working fine. Can somebody help to assist what exact cause of an error. What I'm doing wrong?

static internal bool ExportToDXF(string strFile, string strDXF, IpfcAsyncConnection conn)
{
if (string.IsNullOrEmpty(CreoPath))
return false;
IpfcModel model = null;
try
{
var dxf2d = (new CCpfcExport2DOption().Create()) as IpfcExport2DOption;
int drwtype = (int)EpfcModelType.EpfcMDL_DRAWING;
var session = conn.Session as IpfcBaseSession;

var drwmodelDesc = new CCpfcModelDescriptor().Create(drwtype, strFile, null);
model = session.RetrieveModelWithOpts(drwmodelDesc, new CCpfcRetrieveModelOptions().Create());

try
{
dxf2d.ExportSheetOption = (int)EpfcExport2DSheetOption.EpfcEXPORT_ALL;
var exi = dxf2d as IpfcExportInstructions;
model.Export(strDXF, exi);
}
catch (Exception ex)
{
Console.WriteLine(ex.ToString());
return false;
}
return true;
}
catch (Exception ex)
{
Console.WriteLine(ex.ToString());
return false;
}
}