I've been puzzling over this today. Google does not find any help file for Reader XI (at least not from Adobe: a third party has a PDF "free guide Adobe Reader XI - Visual Steps" but it's too elementary to suit me). Oddly enough, Adobe does still have a PDF for Reader X. Perhaps this is part of Adobe's effort to herd the flock toward the DC pasture, but the grass isn't any greener there I'm afraid.
So far my best suggestion for the "Online Help content cannot be displayed" issue would be to make the following link a bookmark/favorite in your browser: Reader Help | Reader XI help topics. I don't know if that's the link that F1 would theoretically open, but it looks helpful anyway. And I would uninstall Help Manager since it cannot provide help tailored specifically for Reader XI.