Working ok for me this morning, I am using Windows 7 and IE 11.
In their website help section they say they support:
Internet Explorer 11
Chrome (latest two versions)
Firefox (latest version)
Safari 10
They say they do not support:
Internet Explorer 10 and earlier
Chrome (any earlier version)
Firefox (any earlier version)
Safari (any other version)
Opera (any version)
Other than that, I can only suggest the usual sort of thing - clearing cookies and browsing history etc.