I think I finally tracked down the bug that was affecting IE users - you should now be able to sign in and use the site. I've only had chance to test with IE 11 but it should work with IE 10 as well, I'm not sure about IE 9 and IE 8 or older is doubtful.
Fingers crossed we get some replies from IE'ers
NOTE: There may still be other issues but the first and biggest hurdle is getting signed on.