Many a times, it so happens that you need to work with multiple credentials while uploading/downloading apps on Google appengine. In such a scenario, it becomes difficult to switch credentials instantly.
For instance, you have just uploaded an app using appcfg.py with your google credentials and they are still stored in the cache. So when you want to upload a new app, it won't ask you for email/password and still try to retrieve old credentials automatically ignoring any command-line parameters you have given! Thus, you keep scratching your head as to why you are getting a permission-denied error while uploading/downloading the app!
The only way out here is clearing the credential cache of appcfg. On Linux systems, these are stored in a file called:
On Windows based systems, these are typically stored in:
Just delete this file and you are done! Next time, appcfg.py will ask you for a fresh google email and password, thus enabling you to upload/download your app.