updating user field from a plugin

[Data-Base]

hello,

I was searching online for a solution but no luck.

hope some one can help me with it

ok

my site is like this http://www.domain-name.com/
my forums http://www.domain-name.com/forums/

i made the plugin like this:

1- I went to adminCP and created a new PLUGIN I called it "Update User's Information" then I added this line

PHP Code:

include('../user_update.php'); 


2- the option with creating the plugin is:
*Product: vBulletin
*Hook Location: login_verif_success
*Title: Update User's Information

3- I created the file user_update.php in the root http://www.domain-name.com/

4- In the file user_update.php I add these lines:

PHP Code:

// Usre ture::field7

$userfields = array('field7' => "22");
$userdata =& datamanager_init('User', $vbulletin, ERRTYPE_STANDARD);
$userdata->set_existing($vbulletin->userinfo);
$userdata->set_userfields($userfields);
$userdata->save(); 


this field is a custome one I created it with adminCP:

User ture is a Single-Line Text Box with the options (Searchable, Members List) only and the field is (field7)

so now why when I login it dose not update my info !?!?!?!?!?!?!?!?!?

I'm very new to VB but I work with php.

hope some one give me a help to understand it and don't give me links becouse I checked it all.