An unknown error has occurred. E01 – WP Customer Reviews

Hello,
I have installed the following plugin “WP Customer Reviews” v.3.0.8 from gowebsolutions. I keep getting this same error message that keeps appearing when I try to post a review from the plugin. This is the message: “An unknown error has occurred. E01” I deactivated all the plugins in the website and left only the plugin to try and see if it will work, but it did not. I use the following theme for the website: the7 from dream theme

I tried the same plugin on another WordPress that I have and it was working fine. I think it might be an ajax error but it is hard to tell.

I want to ask for support the WordPress community if possible so that I can make the review plugin work

Thanks for the help

Here is the link for the page where I have allowed the review option for the plugin:
http://juno.si/en/