This error can occur when connecting to a secure (HTTPS) server. It means that the server is trying to setup a secure connection but, due to a disastrous misconfiguration, the connection wouldn’t be secure at all!
In this case the server needs to be fixed. Chrome won’t use insecure connections in order to protect your privacy.
You may find that the site works in other browsers. This is because other browsers, unknowingly or intentionally, work around the broken servers. But this doesn't change the fact that the servers have a glaring security hole and should be fixed.
This error message is triggered if the SSL/TLS handshake attempts to use a public key, smaller than 512 bits, for ephemeral Diffie-Hellman key agreement.
For website administrators
If your website has this problem, either: