Can anyone explain why IE on Windows 2012 doesn't show the lock icon despite using HTTPS when visiting the following site?
I am able to see the lock icon on Facebook and any other site.
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It's because the connection is not actually secure: There is an HTTPS error on the page about mixed content. Some data is loaded over HTTP (and not HTTPS), which causes this error. You can see this if you open the page in another browser like Chrome.
Edit: Some more information about mixed content errors, from my answer on this question.