Custom Heading Image not uploading

I’m trying to upload my site’s logo under the Custom Header section. The logo file is a 480x150px png, as directed. When I choose “Crop and Publish”, I get directed to a page with the error message “Oops! That page can’t be found.”

I’ve also tried selecting “Skip Cropping, Publish As Is”. I’ve tried uploading a new logo file, and also tried deactivating all my plugins. Still no luck.