If you're getting an error message "You cannot edit this post" or sth like that, I've had that too. I assume it happens when Nikos is doing some maintenance work. But usually that error message isn't accurate. If you click on "Main Menu" and go back to the post you were trying to edit (in other words, don't click "BACK" on your browser but just move on to Main Menu then the thread), chances are you'll find your edit went through. I find the same to be true when I get the "Page Cannot Be Found" window, both when editing or submitting a post or PM.
HTH.