I've got a booking with China Southern LHR-SYD return in November and I'm having some problems with their website, specifically trying to reserve a seat. When I get to the page and try to choose I get this message

'We could not find your ticket information or Your Boarding Pass has been issued already.Please check-in at the counter with your necessary documents.'

My booking is there and all looks fine so can anyone shed any light? Happy to call them but just wondered if this is perhaps a website problem or if I will have more luck nearer November?

I'm not finding it the most user friendly website

Thanks in advance.