UTIL-PARAM STRING ERROR when calling a form function from a parent form

UTIL-PARAM STRING ERROR when a form function from a parent form.

Error message pops up when calling a child form from a parent form using FND_FUNCTION.EXECUTE.

e.g.

v_param1 := Name_In('XXBLOCK.XXITEM1');

v_param2 := Name_In('XXBLOCK.XXITEM2');

v_param3 := Name_In('XXBLOCK.XXITEM3');

fnd_function.execute(

FUNCTION_NAME=>'CHILD_FORM_FUNCTION',

OPEN_FLAG=>'Y',

SESSION_FLAG=>'Y',

OTHER_PARAMS=>'FORM_MODE="ITEM"'||

'ITEM_NAME="'||v_param2||

'"ITEM_DESCRIPTION="'||v_param3||'"'||

'INVENTORY_ITEM_ID='||v_param1

);

BLOCK.ITEM reference is invalid

Cause : There is no Form Item XXITEM1, XXITEM2 or XXITEM3 in Form Block XXBLOCK, or there is no Form Block XXBLOCK.