Okay, i fixed this myself
My Solution:
Open 'XenForo/DataWriter/User.php'
Find:
'secondary_group_ids'
=> array('type' => self::TYPE_BINARY, 'default' => ''),
'display_style_group_id'
=> array('type' => self::TYPE_UINT, 'default' => ''),
Change to
'secondary_group_ids'
=> array('type' => self::TYPE_BINARY, 'default' => SECONDARYGROUPID),
'display_style_group_id'
=> array('type' => self::TYPE_UINT, 'default' => SECONDARYGROUPID),