This is typically a server-side issue, and not something you can resolve on your own.
The issue is that you're trying to access a site (m.hotmail.com) using a secure connection. Part of that security is a check that the site that responds is the same as the one you asked for. This is done via a series of security checks including a 'certificate' that validates the connection.
In this case, your client is saying that it couldn't verify the connection. This could be for a number of reasons - a problem on the server (e.g. an out of date certificate, a name mismatch, etc.), or it could be because something/someone is intercepting the connection.
There's no way to tell from the error message what the specific case is.
The Cancel button does cancel the connection attempt, but it's likely that the application simply retries, triggering the same error message.