Customer Registration - Access Usergroup Invalid

-- HikaShop version -- : 2.6.0
-- Joomla version -- : 3.4.4
-- PHP version -- : 5.4.45
-- Browser(s) name and version -- : firefox 40.0.3

Hello,

I having the following message when I try out the customer registration:

"Access Usergroup Invalid"

I have set up a group named customer, sub group of registered in Joomla. This group contains 5 groups.
In Hikashop I ad a custom field using the FTW plugin. I have tried different settings and went through the configuration again an again, but it seems I miss something.
Perhaps you guys have an idea.

Thanks

Here the scrennshot

Thanks a lot for the help. It works now.