The significant part of the browser message:
While trying to retrieve the URL: http://serverfault.com/questions/388858/how-to-fix-file-name-too-long-error-in-apache2 The following error was encountered: Access Denied.
I've had this a few times over the last few months or so. Clearly not all is well in SF world.
If this is happening because the question being edited, moved or closed then I'd expect to see a more intelligent and user friendly message.
403from a main Question/Show page? We're not seeing anything like that in the logs for your account in the last week. If you see it again, would you take a screenshot, please? It could be our load balancer config is having issues.