Can't Establish Secure Connection

Hi, 

On a number of website I receive the error 'can't access because a secure connection can't be established'. 

This is the same as the below query - 

https://community.virginmedia.com/t5/Forum-Archive/quot-This-site-can-t-provide-a-secure-connection-quot-error/td-p/4841541/page/2

I have, however, ensured web safe, virus blocker etc are all turned off. I've also tried rebooting the wifi. Could someone help please? All websites worked fine this morning. 

Thanks,