Error codes overview
If you have trouble with your NemID when you either need to log in or sign in, you can find an overview over the known NemID errors here.
Technical issues with NemID
If you have a private NemID and need help from NemID, you can find their support page here. You can find their contact information here.
If you have an employee NemID, you can contact your administrator or the person that issues the employee NemID. Or you can find support here (the page is in Danish).