AppController Not Found

[atypicalconsortium]

I seem to be encountering this with most of the pages. It goes something like, "UTC] PHP Fatal error: Class 'AppController' not found in /home4/gemthaco/public_html/folklore/shop.php on line 5"

I am not familiar with Mysidia at all, but none of the pages like the shop work---it just tells me there's a 500 error when I try to load the pages.

Any help would be appreciated. Thank you!