TimF1975 it might be a system glitch, For the 2 flights I have taken after 3/3 I was not able to select E+ seats by logging in, but I could choose E+ seats when I was not logged in and going to the regular check in page. Also when I was logged in my profile would show my old seat in E- , but when I was using the regular check in page I would see my new seat in E+. You should check to see if that is the case.
Just go here (the regular check-in page) when you are not logged in and try it.
http://www.united.com/travel/checkin...LangCode=en-US