We use SSL (Secure Sockets Layer) when you login to the site.
This is a good thing because your login details are encrypted as they pass over the internet.
The site uses a technology called SNI (Server Name Indication) to do this. Your browser does not support SNI. That means you will see a certificate error when you try to login because your browser does not know how to ask for the correct certificate.
You can safely allow your browser to ignore the certificate error. Your login details will still be encrypted when you access the site.