SQLite.Net Extensions - Don't know about Systems.Collections.Generic.List

I am creating an app using Xamarin with SQLite.NET being used for the local database. I am getting the error message "Don't know about Systems.Collections.Generic.List`1" whenever the database attempts to create a student or register table.

Below is the code for the student and register classes, I have tried to use the SQLite.Net Extensions to allow the tables to be created, but get the error both with/without it.

public class Student
{
    [PrimaryKey]
    public string StudentID { get; set; }
    public string Username { get; set; }
    public string FirstName { get; set; }
    public string LastName { get; set; }
    public string Image { get; set; }

    [ManyToMany(typeof(RegStudent))]
    public List<Register> Registers { get; set; } 
}

public class RegStudent
{
    [ForeignKey(typeof(Student))]
    public string StudentID { get; set; }

    [ForeignKey(typeof(Register))]
    public string RegisterID { get; set; }
}


public class Register
{
    [PrimaryKey, AutoIncrement]
    public string RegisterID { get; set; }
    public string Name { get; set; }
    public string Type { get; set; }
    public string Location { get; set; }
    public DateTime Date { get; set; }
    public string StartTime { get; set; }
    public string EndTime { get; set; }
    public Boolean Recurring { get; set; }

    [ManyToMany(typeof(RegStudent))]
    public ObservableCollection<KeyValuePair<Student, string>> StudentList {get; set;}
}

The connection to the database is made correctly, and the first table is created normally (as it does not contain lists and only strings). I am not sure why this error still occurs even though I have added in the SQLite.Net Extensions code. Below is the code where the tables are created (this is within the constructor for the database):

try
        {
            //Now that the connection has been made, try to create the tables if they do not already exist.

            _connection.CreateTable<User>();
            System.Diagnostics.Debug.WriteLine("Created user table!");
            _connection.CreateTable<Student>();
            System.Diagnostics.Debug.WriteLine("Created student table!");
            _connection.CreateTable<Register>();
            System.Diagnostics.Debug.WriteLine("Created register table!");

        }