I delete 2 "fade in" elements and click "manage details" under flights, it will open the drop down menu for "update passenger details", when update passenger details, Leave " frequent miler info" blank, then it pass through.

Works for P2 flight but not mine, I still get same error after update "The same frequent flyer number has been entered more than once. Please validate your entries and try again. (1302)"

For booking middle seats, I twitter msg Qatar, they won't help, call Qatar NA CSR, call pick up immediately and was done in few mins.