When I try to edit my question, I get a page not found error.
Now it works again. But this wasn't the only error. I've tried to answer my own question, and it gave another error message.
It is an intermittent bug, on the order of 5%. It has been like that for 1-2 days.
The work-around is to save the edited content somewhere, go back to the original page, press edit, paste in the saved content and try again.
What is the URL you are taken to which produces the 404?
I can edit questions I have posted without any issue...