As of June 23 2018, the CAS website SciFinder is blocking incoming traffic using TLS 1.0 protocols. Connections using TLS 1.1 and 1.2 protocols are still supported.
This TLS issue is completely independent of the version of ChemDraw being used. The issue originates from Windows 7 and 8 not being enabled on the client side for TLS protocols 1.0 and 1.1. This is a setting in the System Control Panel and is not browser specific. Find Internet Properties > Security tab; and scroll down in the listing to check "Use TLS 1.1" and "Use TLS 1.2" options. This is not an issue for Chrome or IE 11. IE 11 switches on these additional protocols.
For more information: : https://blogs.msdn.microsoft.com/kaushal/2011/10/02/support-for-ssltls-protocols-on-windows/