Can't passing a parameter WinForm

I’ve an object called "Catalogo" that’s an array of other objects, i use it in Form1 and i wanna use the same instance in Form 2, but I can’t pass it as a parameter, the compiler gives me the error CS0051, but I’m not able to find where I wrong. Can someone help me? That’s my code:

Form1:

public  partial class Form1 :  KryptonForm
    {
       Catalogo  main = new Catalogo();

        public Form1()
        {
            InitializeComponent();
        }


        //when I click the button, create and open a new form2, passing main as a parameter
        private void KryptonButton1_Click(object sender, EventArgs e)
        {
           
            Form2 form2 = new Form2(main);
            form2.Show()
        }




}

Form 2:

public  partial class Form2 :  KryptonForm
    {
      

        public Form2(Catalogo test)
        {
            InitializeComponent();

        }


}

Catalogo class:

  class Catalogo
  {
     public Catalogo()
     {
      //constructing method
     }

  }

Thanks to anyone who will help me!

>Solution :

Make Catalogo accessible (i.e. public)

public class Catalogo
{
    public Catalogo()
    {
        //constructing method
    }
}