Katherine,
I have no idea but I suggest contacting Canvas support about it so they can look at your instance of Canvas. Click on the Help button and select Report a problem, or if you see options for Chat or phone support you can use those (not all schools have that option). That error code makes it seem like something is messed up in Canvas itself and my guess would be that it is with the plagiarism system that you have integrated. That is just a guess though because I can see from the blue rating next to the file upload that one is set up. None of us here in the Canvas Community have access to look at your instance of Canvas but Canvas support will.
Rick
