In SAP How-to document "How to Load a Flat File into BW-BPS Using  a Web Browser V 3.0.PDF", you might notice there are no Chapter 11 and 12 as indicated in Version History. although March 2006 version PDF file can be found, the "Chapter 12.3: Fix for CX_SY_REF_IS_INITIAL exception. Change Event Handler: OnInitialization " part is still missing.

Fortunately the system files are archived in SDN -> Articles (by date), then the new code is:

* event handler for data retrieval
 
* call initialization here
call method application->initialization(
     runtime    = runtime
     page       = page
     request    = request
     response   = response
     navigation = navigation
     version    = 300
     ).
 
runtime->keep_context = 1.