External registration

[zero_ZX]

Hi,
So I got my data manager:

$userdata =& datamanager_init('User', $this->vbulletin, ERRTYPE_ARRAY); 
                            $userdata->set('email', $this->vbulletin->GPC['email']); 
                            $userdata->set('username', $this->vbulletin->GPC['username']);
                            $userdata->pre_save();

But when I try to register it tells me that I cannot leave my email and username empty.
I'm not quite sure about why GPC clears my post data, any help is much appreciated.