[jcasanova]

When I use $crud->callback_insert(array($this,'insert_newuser'));

how can I give back an error to the form and stop the process??

is it possible??

[web-johnny]

For now it is not possible to return a string for an error for callbacks (except the upload callback) . The only thing that you can do is to return false and have a generic error. If you want to give a more specific error the only way to do it right now is from the set_rules as a callback.