I just had the same problem. I'm using OS X with SFML 2.0. There are definitely no other versions of SFML on my machine (I have only installed one version). My app was running fine and then, with no changes to the code, it started crashing in sf::Keyboard::IsKeyPressed().
One possible clue: I'm using the Apple wireless keyboard, and my batteries are getting low. I received a low battery warning around the time that this problem started happening. So I turned off the keyboard and installed new batteries. The problem remained, so I logged out and back in, and the problem was fixed.
So I'm not sure what the problem was exactly (batteries or something else), but there seems to be something keyboard-related that is reset when logging out and back in.