Is TLS v1.0 disabled on the target server? The current version of the agent only uses TLS v1.0. That version is upgraded in the next release that is in Release Candidate status now.
EDIT: You can check with the references in this article - https://support.microsoft.com/en-us/help/187498/how-to-disable-pct-1.0,-ssl-2.0,-ssl-3.0,-or-tls-1.0-in-internet-informa… See also http://www.fastvue.co/tmgreporter/blog/how-to-enable-and-disable-ssl-tls-versions-on-forefront-tmg
I've had a couple that I've had to uninstall the agent and then reinstall it.