same here...
just get the "please sign in" when trying either /limitededition or /redeemcode
have tried loging in with email address instead of username (as suggest on EA's support site)
have tried clearing cache/cookie/all
have tried signing in before loading the code-entry pages (after a cookie/cache wipe)
have tried multiple web-browsers (with all of above)
still just get "please sign in..."
also can't sign in to the game's login either

(have even tried email instead of username - both sign in here fine)