Hi Dag:
Modify your flat file schema to do the following:
1) In the nodes for Header Line and Item, set the Max Occurs property to unbounded and keep the Min Occurs property blank
2) In the node for Posting, set the the Max Occurs property to unbounded and the Min Occurs property to zero (0).
3) Add a sequence group node to your schema, under the Root node, set its Max Occurs property to unbounded, and place all the Header, Item and Positing nodes (mentioned above) underneath this sequence group node in this order: Header, Item, Posting.
Hope this works,
Daniel.