In a Python class I'm teaching, I had the students do the Django tutorial with some added bits. One of the added bits was to add an About page using Django flatpages. A couple of students had problems where they were getting 404 errors even though there was a flat page defined at the /about/ URL.
I had one student zip up his project (including his sqlite database) and send it to me. (One of the other "added bits" was that they had to create portable projects - no hardcoded paths in settings.py.) When I first ran his project, sure enough - 404. I poked around, and everything looked good. Then, I used manage.py loaddata to load my data (including a flat page) into his DB, and it all worked fine. So, it was a data issue, not a project-level mis-configuration.
After reading a comment from another student about this problem, I looked into the database using SQLite Manager, where I could see that the flat page was assigned with site_id #3, not the default #1, and somewhere along the line he had created multiple sites in his DB. I looked in settings.py, and sure enough, SITE_ID referred to site #1, not #3 As noted in the flat pages docs, this needs to match (under some circumstance). Changing that, fixed it all up with the students original data.
If you have been having this problem, I am hopeful that the Google sent you here, and you can see how to fix it.