Hi,
Sorry for the short answer. Add /sap/bc/gui/ to "parameter setting " of the gateway,
SRCURL=/sap/bc/gui/
Use following link see more details of the config webdispatcher.
http://help.sap.com/saphelp_nw73/helpdata/en/b0/ebfa88e9164d26bdf1d21a7ef6fc25/content.htm
Regards