Permalinks Setting 404 Error

Whenever I set my permalink settings to “Post name”, my pages and posts have a 404 error, but my classes and trainers (another 2 types of pages included in my theme). However, when I change my permalink settings to “Numeric”, my classes and trainers pages show a 404 error, but my posts and pages work perfectly well.

I have tried reformatting my server and deleting the .htaccess file but the error still persists.