Help please!
My situation appears to be the same however, going to Settings > Sign Out does not solve the problem.
My iPhone's *AppStore* shows that I need to update 104 Apps. The ID showing is my old Apple ID (in the past, an ID did not requiere the name@domain format; a "xname" was enough).
Recently (due to an IOS upgrade?) my old ID (format "xname") appeared and does not let me change it anywhere! Even in the managing your ID Apple web page that old ID does not show (of course now I have an xname@icloud.com and an xname@me.com besides my xname@domain.com) so how can I get rid of this
Interestingly, if I want to add ('Purchase') a new App my current ID works, but to Update, the old one is hardcoded on the "Sign In To iTunes Store | Enter the Apple ID password for 'xname' "
iPhone 4S IOS 7.1.1 (11D201)
iTunes (on MacBook Pro) 11.1.5 (5)