From the original page:
http://www.ceair.com/server/asr.html

All locales seem to be poorly/bad translated. So I use the Chinese one and Google Translate to get a better idea.

It says "1. Site your seat reservation service is only available at the beginning of ticket numbers 781 and 774 East on Air China-operated ticket.
2. Support the actual carrier China Eastern Airlines include (FM), China Southern Airlines (CZ), Xiamen Airlines (MF) code-share flights."

So you cannot basically select seat online with a non 781/774 prefixed e-ticket number.

Both my name and surname includes spaces, and I had to not input those also. So basically GutierrezArena/JuanManuel worked (format... not my real name )

Now... even tho I get to see my flight legs and two buttons: Reserved Seat and Preferred Seat.

Not sure what of those do, because when I click Reserved Seat, I get to a page that keeps getting me back to the listing page of my flight legs (...) and when I click Preferred Seat, it asks me to login with a MU FF account, which I don't have.

It seems someone at TripAdvisor got luck into using this... https://www.tripadvisor.com/ShowTopi...Air-China.html but so far, no luck for me. I guess I'll have to call.

BTW, my ticket is MU-ticketed, not DL. But I'm a DL PM member.

My ticket has 4 legs, B-Q-Q-B are the fares. Wondering if anyone here had luck into DL thinking all 4 were B fares?

Thanks!