I recently began seeing this error when deploying symfony 2.6.11 to Google App Engine:
ERROR: (gcloud.preview.app.deploy) Error Response: [13] An internal error occurred
In case anyone else sees this, I wanted to post my solution here. I deleted the following file:
vendor/symfony/symfony/src/Symfony/Component/Finder/Tests/Fixtures/r+e.gex\[c\]a\(r\)s/dir/bar.dat
And now the app deploys just fine. This is a test fixtures file, so it's okay to ignore. I suggest updating app.yaml to ignore this file using the skip_files parameter:
skip_files:
- (.*/)?Tests\/Fixtures\/(.*)
NOTE: I assume this is only breaking for the bleeding-edge deployment of gcloud, and will be fixed soon.