 

The ClearItems method empties the Items Dictionary in an OrderForm.
HRESULT ClearItems();
None.
<commerce.h>
After removing the Items collection, ClearItems creates a new ISimpleList instance that represents an empty Items collection. Subsequent additions to the Items collection are made internally through this ISimpleList interface pointer. The HRESULT returned by ClearItems is the result of ClearItems' attempt to instantiate the new ISimpleList interface pointer.