Google announced on Google+ that they are discontinuing support for the AdWords Editor version 10.6 or older. Google is encouraging all advertisers who use the AdWords Editor to upgrade to version 11.1 by June 30th, 2015.

In December 2014, Google launched a major revamp for the AdWords Editor, version 11. It is so different that Google must be finding it inefficient to manage version 10.x, so they are going to stop supporting 10.x and make people migrate to version 11.x.

Google said on Google+:

You can upgrade over here.

Forum discussion at Google+.