get error that site is not working when adding URL

one of the users on my site was trying to add his website to the sites module and was getting an error saying that the site seems to be not working, yet the site is up and fully functional.  He is unable to add the link.  I have also tried to add the site as admin and I receive the same error.

How does dolphin check that the site is up and working, and is there a way to bypass this check.

Thanks in advance and I apologize in advance if this has been asked before

Please try to reproduce the problem on demo.boonex.com ?

Also what is the exact error you are getting when adding the site ?

Check if you have cURL extension installed/enabled on your server, probably it uses this feature.

I did not reproduce the problem on demo.boonex.com and the error that I get is:

As far as the cURL extension, how would I check for this. This one particular site is the only one that has given any users an issue

 /administration/host_tools.php

Thank you dolphin_jay, I did check and yes cURL is installed and active

I would suggest to ask your hosting support to check if outgoing connection is allowed from your site backend.