Most likely reason for this error is that there is a permission issue with the Java installation. Are you sure that NetBeans/TMCbeans is properly using the portable java installation?
Basically it fails to check the ssl certificates for a properly secured connection.
One really bad solution would be to use
http://insecure.testmycode.io/mooc as the server address. However it does make all messages between TMC plugin and server clear text and easily readable for anyone sniffing your internet traffic. Thus exposing your password and submissions...