problems creating a new contact list

first of all: sorry for my bad english. I hope, you'll understand what my problem is... :blush:

If I want to create a new contact list I can't a any user, because the list is empty (see picture). Do I have forgotten something in the configuration?

Do you use special or own defined Joomla groups?

I use own defined Joomla groups.

BTW.: I solved the problem - but don't ask me how :silly: I've changed some settings and suddenly I've had a list of the users. But thank you for your quick reply!