So, in future, if you ever get the following error when submitting a form (with enctype=”multipart/form-data”):
500 Content disposition corrupt: Content-Disposition: form-data; name=""
The error is (and this will affect all non-IE browsers) that you have a form element with a blank name attribute, or a non-existent name attribute. So, do the smart thing and don’t typo your forms, and name all your form elements. Or you’ll spend far too long figuring out what’s a really stupid error, like I just did.