I have been given this message when trying to enter sites I have used for years. I got out of complete lockdown by swqitching off PC and router then a long re-boot. So I can get some sites but others are still forbidden- Very strange. (Did a scan but no problems found)
I assume you’ve googled this problem. I had a quick look as I’d never heard of this error code. Every suggested solution seems different. One suggestion looked incredibly simple and others lost me in a mish-mash of technical jargon. I hope someone else on this forum can be more helpful for you.