I have a Github pages website for our team at http://olinaeromarketing.github.io/. I've tried opening index.html locally and it works perfectly in chrome on my pc. Everything loads perfect. However, when I push everything to Github and try to open it with http://olinaeromarketing.github.io/, everything except index.html gives a 404 error and can't load. I'm pretty stumped as to why this is happening. I also haven't been able to find anything on the web regarding this issue.
The repository is located at https://github.com/OlinAeroMarketing/OlinAeroMarketing.github.io. BTW, the website is currently a WIP and not yet finished.
By default, Jekyll is used to process GitHub Pages. Files/directories that begin with an underscore have special meaning for Jekyll and are, therefore, treated differently.
Since you don't seem to be using Jekyll, your simplest solution is to add a file named '.nojekyll' to the root path to disable Jekyll functionality.
Check out https://help.github.com/articles/files-that-start-with-an-underscore-are-missing/ for more info.
Edit: Just to be clear, the offending directory is '_include'.