We started receiving this error recently. Our API has been working for over four years. Did something change on the DEMO website?
Caused by: java.net.Sock
Per DS Support, DocuSign has ended support for TLS1.0 in Demo from May 29th, 2018 and will soon end the support in PROD as well. Please test the connection on your end if you are using TLS1.0, if yes then you need to upgrade it to TLS1.1+
to again start using DS APIs. I am assuming if you have not done any code changes then this is the issue which you are seeing in your application.