app engine go deploy failed - google-app-engine

Question

It works well yesterday afternoon, but it does not work now.
I use goapp deploy MY_DIR/app.yaml to deploy, and this is the message of deploy
02:38 PM Host: appengine.google.com
02:38 PM Application: MY_APP; module: MY_MOD; version: MY_VER
02:38 PM Starting update of app: exp-lkl, module: MY_MOD, version: MY_VER
02:38 PM Getting current resource limits.
02:38 PM Scanning files on local disk.
02:38 PM Scanned 500 files.
02:38 PM Scanned 1000 files.
02:38 PM Cloning 1085 application files.
02:38 PM Compilation starting.
02:38 PM Compilation: 1081 files left.
02:38 PM Compilation completed.
02:38 PM Starting deployment.
02:38 PM Checking if deployment succeeded.
02:38 PM Will check again in 1 seconds.
02:38 PM Checking if deployment succeeded.
02:38 PM Will check again in 2 seconds.
02:38 PM Checking if deployment succeeded.
02:38 PM Will check again in 4 seconds.
02:38 PM Checking if deployment succeeded.
02:38 PM Will check again in 8 seconds.
02:38 PM Checking if deployment succeeded.
02:38 PM Will check again in 16 seconds.
02:38 PM Checking if deployment succeeded.
02:39 PM Deployment successful.
02:39 PM Checking if updated app version is serving.
02:39 PM Rolling back the update.
Error 500: --- begin server output ---
Server ErrorA server error has occurred.
--- end server output ---
I tried also:
1/ update sdk to the lastest version
2/ update go version (I tried go1.6 and go1.8)
3/ use appcfg.py
But I get the same error
Someone can help?

Answer 1

Finally I fixed this issue.
It seems that app engine changed the error message for the no buildable code. My project does not build, app engine showed the path of the no buildable code before, but now app engine returns 500 error
Error 500:
--- begin server output ---
<h3>Server Error</h3><p>A server error has occurred.</p>
--- end server output ---