This error may occurring if website uses Incapsula for maintaining traffic.
Incapsula provides every website, regardless of its size, with an enterprise-grade PCI-certified Web Application Security, ensuring your website is safe and available.Upon completion of the DNS changes, as outlined by Incapsula, you are effectively directing all of your traffic via Incapsula’s network of proxy servers (Incapsula proxies). Incapsula proxies access your servers directly, and then serve content to the site visitors. Requests to your servers are therefore all coming from a limited range of Incapsula IP addresses. This may result in being classified as attack traffic by various traffic limiting mechanisms and denying Incapsula from accessing your servers.
To ensure that traffic to your website passes through Incapsula, you can limit access to it from non Incapsula IP addresses.
In order to do this, a set of rules should be applied to your firewall (or to your .htaccess files) that will block all traffic coming from non-Incapsula IP addresses.In the case of a firewall or rate limiting mechanism that is blocking access, please contact your hosting provider to whitelist Incapsula’s IP ranges.
220.127.116.11 – 18.104.22.168
22.214.171.124 – 126.96.36.199
188.8.131.52 – 184.108.40.206
220.127.116.11 – 18.104.22.168
22.214.171.124 – 126.96.36.199
This list may change from time to time.
In order to allow all traffic coming from Incapsula IPs and deny any access from non-Incapsula IPs insert the following lines into your .htaccess file:
deny from all
allow from IP1/Mask1
allow from IP2/Mask2