Error: Not Found,The requested URL / was not found on this server.

[fattalgazi]

Hello, when I want to visit my application : http://MYAPPID.appspot.com/

it says:
Error: Not Found
The requested URL / was not found on this server.

what happened to appengine ?

I cant deploy it too, when I try, it says


Starting update of app: MYAPPID, version: 1
Scanning files on local disk.
Error 404: --- begin server output ---
This application does not exist (app_id=u'MYAPPID').
--- end server output ---

[Ernesto Oltra]

MYAPPID cannot be a valid app id. You have to register your own application:

  http://appengine.google.com/

and then change app.yaml or web.xml (Python/Java):

  http://code.google.com/intl/es-ES/appengine/docs/python/gettingstarted/uploading.html

  http://code.google.com/intl/es-ES/appengine/docs/java/gettingstarted/uploading.html