File picker failure creating file and attachment

We’re trying to create a fairly simple control to create a new object, with a file picker for file upload, following this article:

http://help.skuid.com/m/components/l/102564-using-the-file-component-to-add-and-display-images-in-custom-fields

When I select files to use their, it looks like it’s working but then displays “Failure creating file and attachment” - the files are approx 175KB. Interestingly, the three apex api calls that are made from skuid to SF show no errors.