Wrong Case with a few admin files...
I have been trucking through a store install and have gotten a ton of 404 not found pages.. i realized that it was because the cases for the php files that is it looking for, is off:
/admin/options_Add.php when powerstore file(uploaded) is /admin/options_add.php
I have come across a few more but forgot which they were. Mostly when deleted options, products, or renaming them.
/Products_Detail.php --- clicked on the image for the featured product.