Can't use .Add-Function for List

Hi,
I’m struggling with Adding new Elements to a List that get’s serialized afterwards. Getting a bit confused here.
I have a SaveManager.cs storing a List-Class and the Functions for Saving and loading:

public class SaveManager : MonoBehaviour {

    public static SaveManager control;

    public class Error
    {
        public float X; public float Y; public float Z;

        public Error( float newX, float newY, float newZ)
        {
            X = newX; Y = newY; Z = newZ;
        }
    }

    public List<Error> ErrorList = new List<Error>();

    [Serializable]
     public class ListContainer
    {
        public List<Error> error;
    }

    void Awake()
    {
        if (control == null)
        {
            DontDestroyOnLoad(gameObject);
            control = this;
        }
        else if (control != this)
        {
            Destroy(gameObject);
        }

        Load();
    }

    public void Save()
    {
        BinaryFormatter bf = new BinaryFormatter();
        FileStream file = File.Create(Application.persistentDataPath + "/Data.dat");

        ListContainer lc = new ListContainer();
        lc.error = ErrorList;

        bf.Serialize(file, lc.error);
        file.Close();
    }

    public void Load()
    {
        if (File.Exists(Application.persistentDataPath + "/Data.dat"))
        {
            BinaryFormatter bf = new BinaryFormatter();
            FileStream file = File.Open(Application.persistentDataPath + "/Data.dat", FileMode.Open);
            ErrorList = (List<Error>)bf.Deserialize(file);
            file.Close();

            Debug.Log("SaveFile Found and loadad");
        } else 
        {
            Debug.Log("No SaveFile Found. Started Clean"); 
        }
    }
}

Then i have a script for adding the entrys to the list. And there is the problem. I can’ using the Add-Function:

public List<SaveManager.Error> ErrorList = new List<SaveManager.Error>();

public void Create () {  
        float newX = ErrorX;
        float newY = ErrorY;
        float newZ = ErrorZ;
    
            ErrorList.Add(new Error( newX, newY, newZ)); //<- Error: The type or namespace name `Error' could not be found.
}

Any idea why? I guess it’s super obvious -.-

It’s new SaveManager.Error there too. Error is a nested class of SaveManager.