Thanks, I can get something like the attached screenshot, but when I try to add in HKG as a leg on the way back (i.e. SIN - PER - SYD - HKG - SIN, or SIN - SYD - PER - HKG - SIN) it comes up with the error message again.

Was hoping that I might be able to add HKG as a stopover on the return leg with a long layover (if you get my meaning )