Thank you for the screenshot. This issue is caused by your site's CSS theme.
This line causes the problem:
<html lang="en" xmlns="http://www.w3.org/1999/xhtml" dir="ltr" id="vbulletin_html" style="overflow: hidden;">
In order to fix this issue try to add this custom CSS code to your Ecwid theme:
How to add it: http://kb.ecwid.com/CSS-Faq#HowdoIchangeEcwidCSS
If you need any help with this change, let me know.