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JotForm is a free online form builder which helps you create online forms without writing a single line of code. No sign-up required.
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I checked your website and the form does not load sometimes. The form uses a script to calculate the height, seems like this script is failing sometimes, it could be due to a conflict with some scripts in your website or something else. I would suggest you to use the iFrame method instead, you wil avoid this conflict and if you want, you can also set the height by default, take a look on this guide to get the iFrame code: http://www.jotform.com/help/148-Getting-the-Form-iFrame-Code.
Do let us know if it works.