Issue when creating an Item key flex field in a custom form

Hi,

I have created a custom form with one of the fields being system items. I have invoked the flex using the below syntax. But I am not able to bring back the item description. Can anyone help?

FND_KEY_FLEX.DEFINE(

BLOCK => 'LINES',

FIELD => 'ITEM_CODE',

DESCRIPTION => 'ITEM_DESC',

ID => 'INVENTORY_ITEM_ID',

DATA_SET => ':PARAMETER.ORG_ID',

APPL_SHORT_NAME => 'INV',

CODE => 'MSTK',

NUM => '101',

REQUIRED => 'N',

VALIDATE => 'FULL',

USEDBFLDS => 'N',

WHERE_CLAUSE => 'INVENTORY_ITEM_FLAG=''Y''',

ALLOWNULLS => 'Y',

DISPLAYABLE => 'ALL',

INSERTABLE => 'ALL',

UPDATEABLE => 'ALL',

NO_COMBMSG => 'INV_INVALID_ITEM',

LONGLIST => 'Y'

);

Regards,
Kiran