File input Blob.slice error

I've got a form that I'm submitting by ajax, but I guess during the ajax sendoff, I'm getting an error: Can only call Blob.slice on instances of Blob I don't see a console.log immediately after so I assume the ajax is choking?

I create a simple object that contains all the inputs in key/value pairs - shown as the last log entry.

I'm guessing this has something to do w/ file attachments, but I don't know what I've done wrong.