HOW to call an OA Framework screen from Oracle Form???? Please help

Hi Gurus,

I am not sure if I am in the right commuinity or not.

We are in the process of upgrading to R12. Now, I need to call some inquiry forms such as Supplier Inquiry from Our Custom Oracle form. Right now, the Supplier Inquiry form is an OA Framework based. The guideline tells me to call the following way

FND_FUNCTION.EXECUTE
( FUNCTION_NAME => function_name,
 OPEN_FLAG =>'Y',
 SESSION_FLAG =>'Y',
 OTHER_PARAMS => 'partyId='||to_char(:cust.party_id));

But I get an error diplaying in the browser window "You have encountered an unexpected error. Please contact the System Administrator for assistance."