Bootstrap: Preview comments show a pop up window - doesn't work

Hi all,
Any help please? A few users had complained that they weren't able to submit comments. When I click preview comments or post comments button, there is always a pop up window which doesn't show the preview message - a bit annoying at the moment.
The post comments and preview comments button do not seem to work. Any idea on how to fix or disable this.
See screen short.
Thanks for your response.
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