Starting from April 2019, Oracle changed their policy so that you have to sign up for any downloads.

Although signing up is a hassle, because you have to provide personal information and actually remember the ID and passwords, 

the technical side is pretty much tested and proven. I had multiple students sign up and download the .dmg file so it works, at least until now.

The error you are facing seems to be an Oracle server issue, and although I want to help you, I cannot do anything in that regard. 

https://community.oracle.com/thread/3679531?start=15&tstart=0

Try using a different browser, and if all else fails, use a different laptop to sign up, get an ID/password pair and log in. 

Good luck, and let me know how it goes!

Jason.