SSL Certificate error - can't view website

Are you running any anti - virus programs? Using a VPN?

Try setting up another admin user account in System Preferences/Users & Groups to see if the same problem continues. Please post back on whether or not this worked. Also try the Safe Mode. Please post back on whether or not this worked.

Isolating an issue by using another user account 

Safe Mode - About

If it works in the Safe Mode, try running this program when booted normally and then copy and paste the output in a reply. The program was created by Etresoft, a frequent contributor.  Please use copy and paste as screen shots can be hard to read. Click “Share Report” button in the toolbar, select “Copy to Clipboard” and then paste into a reply. This will show what is running on your computer. No personal information is shown. If the log won’t post, try posting it in Pastebin and provide a link in a reply. After pasting the report in a PasteBin page, go to the top of the page, and copy the address in the URL bar. Paste that in a new reply.        Pastebin

Etrecheck – System Information

Found the problem - I hadn't thought to check my hosts file. I moved my client to a new host last year and forgot to delete info from the hosts file after I was done.

Have you tried deleting the site certificate from Applications/Utilities/Keychain Access, then quit/reopened Safari, and see if the site will load?

Try another browser as a test.

Firefox        10.9 or higher

Opera Browser        10.9 or higher

SeaMonkey      10.9 or higher8

Waterfox          10.8 or higher

Did you resolve this issue? I'm having the same problem.

If you did all the above suggested fixes, have you restarted/reset your router?

I'm having the same problem when I switch to using my mobile hotspot. And I have no problem going to the website on any other device on our network.