Hi,
I'm having similar issues to this one:
http://www.gravityhelp.com/forums/topic/failed-temporary-file-could-not-be-copied-help
I have a form with two file uploads (an image attachment and a featured image).
On some cases I'm getting errors. I'm thinking that it might be a memory related issue (timeout, max file size or similar).
The post that I'm linking doesn't say how they solved it. Any ideas or where to start to test?
Thanks