when in the middle of using my email account which was hotmail until recently but was converted to Outlook - I continually get the following message and can not get back in to my email:

"This Connection is Untrusted

You have asked Firefox to connect securely to blu174.mail.live.com, but we can't confirm that your connection is secure.

Normally, when you try to connect securely, sites will present trusted identification to prove that you are going to the right place. However, this site's identity can't be verified.
What Should I Do?

If you usually connect to this site without problems, this error could mean that someone is trying to impersonate the site, and you shouldn't continue.

What is this and how do I stop this from occurring?