Outlook 2010 Encrypted connection to server refused

Willy K

Outlook version
Outlook 2013 64 bit
Email Account
I have two Win 7 systems with Outlook 2010 and IDENTICAL Outlook email IMAP account setups.

Lately, one of the systems can no longer obtain an encrypted connection (SSL/TLS) to the ISP server, both ways (in/out). I'm persistently getting only 0x800CCC0E errors "Cannot connect to the server." The other system works fine, so the problem must be local. However, I can't figure out what's wrong.

I've been through every thinkable setting, did a full MS Office repair, checked my Anti-virus settings (ESET), and even tried to connect with the Anti-virus turned off... Nothing works. BUT IF I TURN OFF THE ENCRYPTION, then the Outlook client (on the problematic system) connects fine with the ISP server both ways! So I suppose that the problem must be related to using SSL/TLS. These are enabled in Internet options, and as far as I can tell there's no difference between the PC that works, and the PC that has the problem.

What could be wrong? Where to look for possible errors?

Any suggestions? Thanks!