I have a few entries which are set to disabled. It seems that the live preview is not working then. It only works when the entry status is enabled.
This seems more like a bug than a feature, right?
I have checked everything again and all conditions stated by Brandon below are met, but now I see that I actually don't use the "entries own url" setting. It's enabled, so I get the live preview button, but I use dynamic routing to create my own url's (because I need to add a category as a segment in the URL).
So that's probably where it goes wrong. I check the last segment of the URI as the slug of the specific entry and set my entry manually by it.
So how do I make live preview work than?