The guys at Activeboard who I pay a monthly subscription to, have in the past few days moved the site over to a secure HTTPS so you shouldn't get anymore certificate errors, but might get 'mixed mode warnings'.
When a site is secure anything in it (images etc) should all be located from a https site. For example I had to change Brads signature image as it was being hosted at tinypic - a HTTP non secure site. So anywhere Brad has posted would cause us all to get the mixed mode warning (I've changed the location to our site). If a page is secure (like your bank) you'll get a green padlock icon or similar in the address bar, if not there might be another icon like a warning triangle)
When writing a post all those little thumbnail icons above the post wrtiting box are not secure, I've sent a message to Activeboard to sort this.
In future just be wary where you get images from or link from as non HTTPS sources will cause all of us mixed mode warnings. I know this is a pain, but blame Google, it's their grand idea that the entire public web should be HTTPS and that's why all browsers (started with Chrome), now check and go bananas if the site you're using isn't HTTPS.
If you come across anything that's giving you a mixed mode warning can you let me know what page it is - so I can see what's causing it.
Further to the lovely reference on MM 'have we croaked it' - no, before MM implemented it MB had a mobile version, and before MM implemented it we now have a secure site, without ads (Ok tried and failed but still).
