There are a couple of other questions that are closely related to this one, but neither of them have answers specific to a Gaelyk application.
When I try to use the appengineupdate Gradle command to update my Gaelyk application to the server, after entering my username and password, I get an error message: "Unable to update app: Bad authentication response: 404 Not Found".
It doesn't take much investigation to find that the error message is due to GAE deprecating their old ClientLogin authentication, and Google says to use new OAuth 2.0 authentication. However, how does one do this for a Gaelyk application? The documentation that exists is not of much help; I couldn't find any instructions specific to GAE or Gaelyk.
This turned out to be not very difficult at all.
In the build.gradle file, update the gaeVersion to the latest version. As of July 2016, it is:
def gaeVersion = '1.9.38'
Then, when you do the update, a Google page will open up, asking you to log in, and then it will give you a code to copy.
The update will wait for you to paste in the code, then the update should complete successfully.