Passing GET value show error

That seems a fair approach but you could use site_url instead, just a bit cleaner.

PHP Code:

<a href='<?php echo site_url('documentazione/crea_documentazione_seconda/'.$row->id); ?>' class='btn btn-primary btn-xs'> 


If pressing that button is causing the missing argument, then just take a look at the html generated for the button and check the id is being found and is populated as you expected.

Other than that I cannot debug your code, sorry.

Paul

PS Looking at your first post again, when you load a view file you are just loading a file, and sending it some data. You are not loading a controller into the view.

PHP Code:

$this->load->view('my_view_file', $page_data); 


If you use a variable in the view file name, you have to be careful that the file actually exists before you load it using file_exists.