Why does Word Press keep going wrong?

After writting a new post when I click publish I often get this message

Word Press Error

Clicking ‘No’ goes back to a blank post form

Clicking ‘Yes’ says the post is published, however when you click ‘Vew Post’ it gives an ‘Error 404’.

I think it only occurs if the post is auto saved, and I think I can get round it by make a new blank post, then going back and editing it.