Used this plugin for a while but it's run its course. Auto-redirecting to HTTPS is no longer reliable and certain elements still try to load as HTTP. But this is to be expected for a plugin last updated in 2012.
Luckily a few new plugins are now available that not only do everything this one does, but do it more reliably. I like "Really Easy SSL". Works flawlessly on the 3 websites I've tested it on so far. Give it a try.
Normally I wouldn't pitch another plugin here but the author has likely abandoned the plugin for the foreseeable future and an HTTPS plugin is something you want to keep up to date. Hopefully this helps.