Salut,

Je ne suis pas un spécialiste d'android mais le build.xml est le script ant qui va faire la compilation.
Tu as essayé de suivre le message indiqué ? A savoir utiliser android update project :

http://developer.android.com/guide/deve … ngAProject

citation :

Updating a Project

If you're upgrading a project from an older version of the Android SDK or want to create a new project from existing code, use the android update project command to update the project to the new development environment. You can also use this command to revise the build target of an existing project (with the --target option) and the project name (with the --name option). The android tool will generate any files and folders (listed in the previous section) that are either missing or need to be updated, as needed for the Android project.

To update an existing Android project, open a command-line and navigate to the tools/ directory of your SDK. Now run:

android update project --name <project_name> --target <target_ID>
--path <path_to_your_project>

    target is the "build target" for your application. It corresponds to an Android platform library (including any add-ons, such as Google APIs) that you would like to build your project against. To see a list of available targets and their corresponding IDs, execute: android list targets.
    path is the location of your project directory.
    name is the name for the project. This is optional—if you're not changing the project name, you don't need this.

Here's an example:

android update project --name MyApp --target 2 --path ./MyAppProject

citation :

If you're upgrading a project from an older version of the Android SDK or want to create a new project from existing code, use the android update project command to update the project to the new development environment. You can also use this command to revise the build target of an existing project (with the --target option) and the project name (with the --name option). The android tool will generate any files and folders (listed in the previous section) that are either missing or need to be updated, as needed for the Android project.

Oui, je pense que c'est effectivement le problème.
Peux-tu essayer de créer un petit sketch test du début et voir si cela fonctionne ?

Et sinon, quelles sont les difficultés qui t'empêchent de lancer la commande android update project ? [je précise que je ne connais pas du tout le processus de création d'un sketch android avec processing]