Make sure that the site or domain are not set in your Comaptibility Mode settings in IE.
Also, make sure that you are not setting the document compatibility mode on the site with any meta tags or http headers. The only exception is that setting an http header with "X-UA-Compatibilble" "ie=edge" is acceptable and will override any users settings that try to force lower version compatibility.
I've read that you can also just start the first line of your html with:
that's mentioned in this article:
I've successfully used the http header method, but I have no personal experience with the DOCTYPE or the meta tag. I've read that some people have said that the meta tag comes too late in some cases to help with the issue though.
I hope that helps.
-Seth