What is JotForm?
JotForm is a free online form builder which helps you create online forms without writing a single line of code. No sign-up required.
At JotForm, we want to make sure that you’re getting the online form builder help that you need. Our friendly customer support team is available 24/7.
We believe that if one user has a question, there could be more users who may have the same question. This is why many of our support forum threads are public and available to be searched and viewed. If you’d like help immediately, feel free to search for a similar question, or submit your question or concern.
I've checked your form and found out that it's integrated to Dropbox. Just so you know that our Dropbox API only supports up to 300MB of File. I think the problem is related to this. Your file upload field currently set to allow 1GB of File.
Please check this guide for more details: http://www.jotform.com/help/33-Changing-the-Upload-Size-Limit.