Safari: "Failed to load resource: cancelled" in console. What does this mean?

I am开发者_开发问答 getting this error in the safari developer console:

Failed to load resource: cancelled

What does this mean? I don't see any errors on the page, so why am I getting this message? I have an iframe on the page that is hidden when it loads, but it loads fine when I display it so I don't know why I'm getting this message.