This looks like a bug, I’ll fix it and get another build up, one thing to note though: It looks like you packaged the Debug version of your project, if you change the packaging configuration to development or shipping you shouldn’t get that error.
It means I’m not handling a particular file type correctly and I should be defaulting unrecognized files to text/plain but I’m not (bug). Just curious: I’ve got mime types for html, png, jpg, bmp, css, javascript is there another kind of file you are loading/referencing in one of your pages?