After a little bit of poking around, I discovered that CompleteSSL had changed their CA to Comodo, and that they are trusted via AddTrust. Interestingly enough, thats the same trust that was in place before. I looked further into it and the CA was the same (even the thumbprint matched - ‎02 fa f3 e2 91 43 54 68 60 78 57 69 4d f5 e4 5b 68 85 18 68), but the new certificate was not accepted still (unknown issuer) .

I installed the certificate found here -https://support.comodo.com/index.php?_m=downloads&_a=viewdownload&downloaditemid=87 as a Trusted CA and the certificate was accepted.

I can't really explain that one, but what a pain in the butt.

Well, its really quite easy. Youtube were kind enough to re-work their embed method from an <object> to an <iframe></iframe> and now fully support HTTPS.

very simply, here's the html you need.

<iframe title="YouTube video player" width="1280" height="750" src="https://www.youtube.com/embed/XXXXXXXXXXXXXXXX?rel=0&amp;hd=1" frameborder="0" allowfullscreen></iframe>

XXXXXXXXXXXXXXXX - embed ID of the video. you can see this in the URL of the youtube video

https -  http or https, depending on if you're embedding from a HTTPS page or not (if the page is accessible via both http and https, use https to avoid an IE security warning)

?rel=0 - realated videos.. 0 = none, exclude or =1 for allow

hd=1 - high definition.. 1 = high def, 0 (or exclude) = standard

1280 - width (1280px in this case.. you probably want it smaller)

750 - height (750px in this case.. you probably want it smaller)

allowfullscreen - exclude if you don't want your users to be able to make fullscreen (self explanatory really)