[Badshah93]

When you updating any existing data using datamanager then you need to call
set_existing function first.

Try This Code: (Run this code after registration is complete)

PHP Code:

$userdata =& datamanager_init('User', $vbulletin, ERRTYPE_STANDARD);
    $userdata->set_existing($vbulletin->userinfo);

        $userfields = array('field2' => $vbulletin->GPC['cfield_2'], 
                                    'field6' => $vbulletin->GPC['cfield_6'], 
                                    'field7' => $vbulletin->GPC['cfield_7']
                             );

        // Saving Userfields Now

        $userdata->set_userfields($userfields);

        $newusergroupid = 9; 
        $userdata->set('usergroupid', $newusergroupid); 

        $userdata->pre_save();  


         if (!empty($userdata->errors))  
        {  
              $errorlist = '';  
              foreach ($userdata->errors AS $index => $error)  
             {  
                  $errorlist .= "<li>$error</li>";  
             }  
      
              // ... additional code; $errorlist is outputted to the user  
        }  
       else  
       {  
             // save the data  
            $vbulletin->userinfo['userid']  = $userid  = $userdata->save();  
          
             // ... additional processing code  
       }