Error 16

There are various causes for that, and the details here matter.

Did you edit out some details on that? Like the identify of the web site, the time, and the IP address and maybe the proxy address that might have been displayed? Maybe an “are you a robot?” question in the displayed web page, too?

If it’s the same web site and other web sites are allowing your access, then it’s probably the configuration of the web site.

Various web site operators use services providing protection against traffic flooding attacks, and sometimes the flooding detection can glitch. Incapsula was one of the service providers, and the error generated by that service is very close to the reported text.

If this is a single web site, then there are various potential work-arounds such as accessing from a different network, or resetting your ISP modem to try to get a different public IP address. Or try again later. Or contact the (usually) vendor and ask. Using VPNs or Tor are potentially also possible here, but various flooding services can or will block those.

If the above guesses are correct, then this likely isn’t local anti-malware.

If you are running any third party app that claims to protect, clean, boost performance, etc., uninstall the app.

Bob beat me to it... running any Anti-Virus Apps?

https://techviral.net/error-code-16-this-request-was-blocked-by-the-security-rules/