[kh99]

Yeah, it's caused by this code in class_upload.php (around line 957):

if (!($result = $this->data->save()))
{
	if (empty($this->data->errors[0]) OR !($this->registry->userinfo['permissions']['adminpermissions'] & $this->registry->bf_ugp_adminpermissions['cancontrolpanel']))
	{
		$this->set_error('upload_file_failed');
	}
	else
	{
		$this->error =& $this->data->errors[0];
	}
}

For some reason if you're not an admin it doesn't use the errors from the attachment object.