is there any reason one can see why "http://www.second-opinions.co.uk/fl...eharm.html" would not be resolvable in AS? FB finds the link fine..

I think we've discussed this before, but resolving the link for preview purposes is 100% dependent on your server environment. The fact that Facebook can resolve the link is irrelevant. If you can't resolve the link or Active Social reports an error then you need to contact your hosting provider. You will want to explain to your host that your site requires a feature that executes a remote HTTP request. This means it makes a network connection to the remote URL in order to capture the full html of that page.