unfortunately MAC OS is not supported as an administration system (see product guide).
Have you tried from a windows or Linux machine with JRE 7 Update 17?
Thanks for your answer, I've regressed JRE 7 back to JRE 6 on Mac OS X ML. Web Gateway 7 GUI always worked OK with that, and that has cured the problem. If I really need to update JRE back to 7 at some point then I can use Windows or Linux in a VM, as you suggest above.