Please don't run around proclaiming:
OLD account from MP DEMO will screw you out of the LE DLC.
that is not true. The LE DLC works perfectly fine for me... Guess what? I'm using my demo account!
The LE DLC page has errors in it and may prevent the activation, that will be fixed.
If you can't login to your account in game it is probably because you are not typing your info correctly.
Besides, all the LE DLC is is some weapon skin that doesn't matter and will be outgrown in the later stages of the game, a pretty lame hologram feature that wastes 5 AR shots from an enemy or team mate who can't tell the difference, a dog tag that doesn't really look cool and I do not even care for and some xp that just puts you to level 5 so you can hit max level 3 minutes sooner than everyone else!