The same here. It’s 2 days since I get an SSL error on Chrome & IE. Now I’ve signed in to twitter using Firefox. The strange side of the story is that non of the settings on my pc/network/wi-fi, I mean nothing, has changed since my last normal twitter visit 2 days ago!
I used another ISP, but useless. And another strange part is that other websites using secure connection (https) like facebook working normally. So we may conclude the problem must be on twitter itself, not our devices/connections.