Each domain goes thru checking the metrics from left to right on your screen. So for your first url it checks facebook, then google, then linked in etc..
Whats happening is that these social urls are used by a lot of programs, including malware and such things. So it appears as if something is blocking access to the linkedin urls. 503 is service unavailable.
I just tried it on a bunch of random urls and it worked fine on all sources. Ive seen this before though. You need to whitelist the addons folder (which is in your scrapebox folder) in all security software such as anti-virus, malware checkers, firewalls etc...
You could also try to whitelist it in your router and/or disabling the router firewall as a test or just bypass it by connecting direclty to the internet or a mobile dongle etc..
But to be sure its something local to your setup and not the addon its self as its working for me on more then a dozen machines.
Just realized you were a moderator, I missed that somewhere along the way way. Congrats!
It shouldn't matter that its on a VPS. I mean I run it on VPS and on dedicated servers just fine.
But your not the first person I have seen this with. There have been a few other folks that have had this issue and they were never able to get it to work, seemingly.
I mean its "possible" that your host is blocking the linkedin request url of course, but not many hosts block things.
Now whats interesting is that I just looked at it in a debugger and the url for linked in that scrapebox is pulling is a http url that redirects to a https url via 301. Ill mail support about that, its probably ideal to have it going to the exact url and not making an extra request on each.
In general 301 is as you know ultra basic so I can't see why that would matter to a firewall or anything, but its possible.
Try it with just like 1 or 2 urls. Taking note that the addons pulls proxies upon start. So if you start it and the use proxies box is checked and then you go back and uncheck the use proxies box, the addon will still use proxies. You have to close the addon and then start it again in order to have it then not use proxies. You may well have done that but its worth mentioning just in case.
Edit: I actually just noticed your still using V1 of Scrapebox. That addon screenshot is the social check for V1, V2 of Scrapebox is completely rebuilt and the addon with it. So that old addon might not even be querying the correct urls.
Then just run it, it will take a min to start up and will ask you for your license email but should then auto attach to your license and work immediately. Install the Social addon checker, does it work?
Also worth noting is that V2 was a complete rewrite of the code with over 1.1 million lines of new code written, so there are a lot of new features you might find useful too. Plus new plugins like the expired domain finder and the yellow pages scraper and lots more. You can check out the change log, V2 has already had 62 updates as well.