Does anyone know why some of the additional pages that I add do not show up? I just get a 404 error.

Sometimes I can change the name and it will show, other I can not get them to show at all.

e.g. I can not get a page with the name abigail_miller to show no matter how I arrange or space the words. Other pages like john_marshall work just fine. Another page I can not get to show is male_quartets.

The site I am working on is GreatGospelMusic.com