Both the Foglight Agent Manager and the monitored host serverEnable TLS v1.2 protocol on the Agent Manager Windows server as described in Knowledgebase article
4310066 .
SQL Server instance on the monitored hostApply critical updates to the SQL Server instances as per Microsoft Knowledgebase article
KB3135244 .
Note: SQL Server 2005 instances cannot be updated to accept TLS v1.2 connections.