Problem with IDL inheritance!

I have a ploblem with IDL inheritance.

module MainObjects
{
interface MainObject
{
attribute wstring src_id;
};

interface ITele : MainObject
{
attribute wstring tele_type;
attribute wstring tele;
};

};

Java code is:

class MainObject exyendes MainObjectPOA
{
....
}
class Tele extends MainObject implements ITeleOperations
{
.....
}

When writing in server:
TeleVector.addElement(ITeleHelper.narrow(_poa().servant_to_reference(tele)));
Corba server comes back with the following message:

org.omg.CORBA.BAD_PARAM: Narrow failed minor code: 0 completed: No

How can I resolve this problem?