Can no longer access drafts

When I tried to save a draft of a post just now, I got a full-screen message telling me I couldn’t because the article was not there.

So far, so strange – but then I could no longer see any of my posts in the backend (although it gives me the correct number in brackets and all remains fine in the frontend). I tried writing a test post, to see if that would jolt the system to its senses. That had some effect – at least now the already published articles are displayed and editable again.

But I still can’t access the drafts. Including any I add from now on. I also can’t access the categories the posts where in. Clearly the post I was trying to save is causing a conflict. But I have no idea how to resolve it…

I use WordPress 2.6.5. (in German).