Sorry to hear that! There are a few reasons why this might happen, both at our end or yours.
Please make sure you are on a solid broadband connection and if possible plug your computer into your router via ethernet rather than wifi. It is possible a wifi dropout can interrupt an upload and cause it to fail.
It is also possible there is something about your media that our servers don’t like. They’re normally pretty good but everyone has their moments, right?
If it happens again and you have verified your broadband connection is solid, you can try re-exporting in one of our recommended formats or get in touch with us using the 'Submit a request' button at the top of this page.
See this article for recommended upload formats: What’s the best format to upload to Wipster?.