Problems with extending CI_Form_validation

How are you loading the validation library?

PHP Code:

$autoload['libraries'] = array(
 'database', 
 'email', 
 'session', 
 'form_validation', 
 'pagination', 
 'encryption'); 


Try using the subclass_prefix MY_

Regarding problem #1, everything looked OK to me the way you handled it in the beginning, except how you refer to the callback function.
Try:

PHP Code:

$this->form_validation->set_rules('email', '', 'callback_scanEmail'); 


The function itself should keep the name 'scanEmail'.

That approach will only look for the method scanEmail in the controller where the rule was set.

Try using the subclass_prefix MY_

if I set the prefix, then I should change my Model and core Controller which I made by myself. which I don't want this happen.

Is this bug? because shouldn't be any force to have a prefix and suppose to work!

If you extend a core library by using the MY_ prefix, the extended library is loaded with the original name. So there is no need for changing your controllers or models.
When you load the Form_validation library, CI will first check if there is a MY_Form_validation.php in application/libraries. If that isn't the case, it will load the core library from system/libraries.