When uploading, the --url parameter must link to the remote_api of your application, like so:
appcfg.py upload_data --application=myapp --kind=Survey --filename="C:\myapp\src\test.csv" --url=http://myapp.appspot.com/_ah/remote_api 
| | I'd add one other note if you are uploading to an app you migrated over to the high replication datastore... add "s~" to the front of your application parameter value. For example, --application=s~myapp |
Read full article from gae datastore - Problem uploading and downloading data from to deployment app in GAE - Stack Overflow
