Hi @jbuchman
Welcome to the Canvas Community.
I've wondered about that warning before. Apparently it means that the page you were trying to reach on a website couldn't be found on their server. How to Fix a 404 Page Not Found Error has more information.
I'm wondering about where you have your powerpoint stored. Might that be the issue?
Here is a guide for uploading a file, perhaps this might iron out the error 404 issue. How do I upload a file to a course?
If you have no luck there then perhaps it's time to contact Canvas Support - https://community.canvaslms.com/docs/DOC-17624-how-to-contact-canvas-support
Sing out if you need a hand.
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