In case of error, what to do:
1) Read the error message! Most of the time the answer is already explained.
2) Run the setup script:
<PHP-INTERPRETER> cw3setup.php --install --base-url http://url/to/your/cartoweb3/htdocs/
3) Run the setup script with clean option:
<PHP-INTERPRETER> cw3setup.php --clean
4) Be sure all files and folders have the correct name
5) Be sure all layers and layersgroups have the correct name
(to complete)