Access to Apple ID Sign-in Page on safari

I am trying to resolve a separate question with the Community on my iMac but need first to sign in with my Apple ID of course.

However, having entered my Apple ID and Password I repeatedly get the message "Safari can't establish a secure connection to the server." or "Safari can't open the page". The Safari on my iMac is Version 6.1.6(7537.78.2)

I can access any other URL with no problem but not the Apple site so it's not a router or internet issue.

I am writing this on my MacBook Pro and have signed in with no problem here.

Any help gratefully received please.