Hi Laurent,
However it does make sense: with the outbound handler enabled you hand off the responsibility of opening the catalog to the outbound handler, which first creates the body of the back button (actually it is the link...) and then opens the catalog in the iframe inside of this page.
See class & method /SAPSRM/CL_CH_WD_OUTBOUND_HDLR ~IF_HTTP_EXTENSION~HANDLE_REQUEST:
* render the back to SRM function as a plain link * provided by JavaScript function to be accessed as inline frame source render_back_link( EXPORTING io_request = lo_request CHANGING cv_html = lv_html ). * alternatively render the back to SRM function as unified rendering HTML * provided by JavaScript function to be accessed as inline frame source * render_back_button( exporting io_request = lo_request CHANGING cv_html = lv_html ). * render the catalog redirection as invisible form with automatic submit * provided by JavaScript function to be accessed as inline frame source render_catalog_redirection( EXPORTING io_request = lo_request CHANGING cv_html = lv_html ).
So that is why I asked you to check on the HTTP calls done - here you can find what service is called and which one returns the failed service call.
Regards,
Robin