Hello Robin,
all seems to be OK in method IF_HTTP_EXTENSION~HANDLE_REQUEST from /SAPSRM/CL_CH_WD_OUTBOUND_HDLR class...
Call to method RENDER_BACK_LINK and RENDER_CATALOG_REDIRECTION is OK (no invalid URL);
Then, at the end of IF_HTTP_EXTENSION~HANDLE_REQUEST, the three methods to write the locally rendered HTML to the response are called (i cannot debug them) without exception.
But after, IF_ABAP_RUNTIME~GET_RUNTIME method (CL_ABAP_RUNTIME class) is called: at this moment i have my first screen-short error...
Regards.
Laurent.