I'im writing a program that works with 2 forms, the main form and the form where the configuration is made, so when the user clicks toolstripmenu->Preferences the Preferences form is showned and I want it to make the user only capable of having one Preferences form at a time.

When I use:

```
    Prefs preferencias = new Prefs;

    private void preferenciasToolStripMenuItem_Click(object sender, EventArgs e)   
    {
        preferencias.Show();
    }

```

It works, but when I close the Preferences form and try to open a new one the program crashes.

And When I use:

```
    private void preferenciasToolStripMenuItem_Click(object sender, EventArgs e)   
    {
        Prefs preferencias = new Prefs;
        preferencias.Show();
    }

```

The user can hav multiple Preferences form.

What can I do?

Thanks in advance.