I'm changing my hosting service and now find that whilst I can add new posts I can't amend any of them.
For the change, I backed up the DB from the old server, restored that on the new one (adding utf8 encoding as suggested elsewhere) and copied the various HTML etc. files across. I also changed the defaults on the new host to utf8 as suggested.
The new setup lets me write new posts but doesn't let me amend them. When I try amending a post, the edit screen comes up fine but when I save it, it goes straight to the domain screen rather than staying within the wordpress software and the changes haven't been saved.