Have you read this Bruno. http://ai2.appinventor.mit.edu/reference/other/appstoplay.html
App Inventor creates its own keystore file. I understand using the keystore from a previous app that you make with a different compiler will not work. You cannot take a keystore from another app and ‘give’ it to your new app created with App Inventor. See the posts from the old Forum about using a keystore.
Regards,
Steve