Google App Engine: "You do not have permission to modify this app"

Common error. Simple solution.

1. Delete file to reset your local credentials used by appcfg
1. Linux: rm ~/.appcfg_oauth2_tokens_java
2. Windows: del /users/.../.appcfg_oauth2_tokens_java
2. Upload!
1. APPENGINE_SDK_HOME/bin/appcfg update war-directory