Description: This error happens when your site generates a 500/501/503 internal server error when we try to scan it. It might be a temporary error, but it can also be related to a malicious injection gone wrong and breaking the site.
If you get this warning, try to run a real time scan here: http://sitecheck.sucuri.net to see if the problem remains.
You can also contact your hosting company for more details (since it could be related to something they are doing).
500 Internal Server Error