String zu einem Secure string konventiren

Hallo Zusammen, ich mache ein kleines Skript mit einem Gui.
Bei einer Textbox wo ich ein Passwort eingeben, kommt immer ich kann den string nicht ihn ein securesafe konventieren

Add-Type -AssemblyName System.Windows.Forms


#### GUI selber
$Form = New-Object system.Windows.Forms.Form
$Form.Text = "PC-Infos"
$Form.TopMost = $true
$Form.Width = 612
$Form.Height = 418

#### Textfeld

$listView1 = New-Object system.windows.Forms.ListView
$listView1.Text = "listView"
$listView1.Width = 398
$listView1.Height = 167
$listView1.location = new-object system.drawing.point(74,184)
$Form.controls.Add($listView1)

#### Benutzer hinzufügen Button

$button1 = New-Object system.windows.Forms.Button
$button1.Text = "Benutzer hinzufügen"
$button1.Width = 147
$button1.Height = 32
$button1.location = new-object system.drawing.point(75,44)
$button1.Font = "Microsoft Sans Serif,10"
$Form.controls.Add($button1)
$button1.Add_Click({
   $form = New-Object System.Windows.Forms.Form

   #### Titel

$form.Text = 'Automatisierung für Benutzer anlegen'
$form.Size = New-Object System.Drawing.Size(500,400)
$form.StartPosition = 'CenterScreen'

   #### OK-Button

$okButton = New-Object System.Windows.Forms.Button
$okButton.Location = New-Object System.Drawing.Point(25,325)
$okButton.Size = New-Object System.Drawing.Size(75,23)
$okButton.Text = 'OK'
$okButton.DialogResult = [System.Windows.Forms.DialogResult]::OK
$OKButton.Add_Click({$x=$TextBox.Text;$Form.Close})
$form.AcceptButton = $OKButton
$form.Controls.Add($OKButton)

  #### Cancel-Button

$cancelButton = New-Object System.Windows.Forms.Button
$cancelButton.Location = New-Object System.Drawing.Point(120,325)
$cancelButton.Size = New-Object System.Drawing.Size(75,23)
$cancelButton.Text = 'Cancel'
$cancelButton.DialogResult = [System.Windows.Forms.DialogResult]::Cancel
$CancelButton.Add_Click({$Form.Close()})
$form.CancelButton = $cancelButton
$form.Controls.Add($cancelButton)

  #### Abfrage 1

$label1 = New-Object System.Windows.Forms.Label
$label1.Location = New-Object System.Drawing.Point(10,20)
$label1.Size = New-Object System.Drawing.Size(280,20)
$label1.Text = 'Benutzername:'
$form.Controls.Add($label1)

$textBox1 = New-Object System.Windows.Forms.TextBox
$textBox1.Location = New-Object System.Drawing.Point(10,40)
$textBox1.Size = New-Object System.Drawing.Size(260,20)
$form.Controls.Add($textBox1)

  #### Abfrage 2

$label2 = New-Object System.Windows.Forms.Label
$label2.Location = New-Object System.Drawing.Point(10,80)
$label2.Size = New-Object System.Drawing.Size(280,20)
$label2.Text = 'Passwort:'
$form.Controls.Add($label2)

$textBox2 = New-Object System.Windows.Forms.TextBox
$textBox2.Location = New-Object System.Drawing.Point(10,100)
$textBox2.Size = New-Object System.Drawing.Size(260,20)
$form.Controls.Add($textBox2)

  #### Abfrage 3

$label3 = New-Object System.Windows.Forms.Label
$label3.Location = New-Object System.Drawing.Point(10,140)
$label3.Size = New-Object System.Drawing.Size(280,20)
$label3.Text = 'Passwort wiederholen:'
$form.Controls.Add($label3)

$textBox3 = New-Object System.Windows.Forms.TextBox
$textBox3.Location = New-Object System.Drawing.Point(10,160)
$textBox3.Size = New-Object System.Drawing.Size(260,20)
$form.Controls.Add($textBox3)

  #### Abfrage 4

$label4 = New-Object System.Windows.Forms.Label
$label4.Location = New-Object System.Drawing.Point(10,200)
$label4.Size = New-Object System.Drawing.Size(280,20)
$label4.Text = 'Vollständiger Name:'
$form.Controls.Add($label4)

$textBox4 = New-Object System.Windows.Forms.TextBox
$textBox4.Location = New-Object System.Drawing.Point(10,220)
$textBox4.Size = New-Object System.Drawing.Size(260,20)
$form.Controls.Add($textBox4)

  #### Abfrage 5

$label5 = New-Object System.Windows.Forms.Label
$label5.Location = New-Object System.Drawing.Point(10,200)
$label5.Size = New-Object System.Drawing.Size(280,20)
$label5.Text = 'Beschreibung:'
$form.Controls.Add($label5)

$textBox5 = New-Object System.Windows.Forms.TextBox
$textBox5.Location = New-Object System.Drawing.Point(10,220)
$textBox5.Size = New-Object System.Drawing.Size(260,20)
$form.Controls.Add($textBox5)

 #### Abfrage 6

#$label = New-Object System.Windows.Forms.Label
#$label.Location = New-Object System.Drawing.Point(10,200)
#$label.Size = New-Object System.Drawing.Size(280,20)
#$label.Text = get-localuser
#$form.Controls.Add($label)

$form.Topmost = $true

$form.Add_Shown({$textBox1.Select()})

$result = $form.ShowDialog()

if ($OKButton.Add_Click)
{
    if($textBox2.Text -eq $textBox3.Text){
    New-LocalUser -Name $textBox1.Text -Password $textBox2.Text -FullName $textBox4.Text -Description $textBox5.Text
    } else {
    $label6 = New-Object System.Windows.Forms.Label
    $label6.Location = New-Object System.Drawing.Point(240,325)
    $label6.Size = New-Object System.Drawing.Size(280,20)
    $label6.Text = 'Das Passwort stimmt nicht überrein'
    $form.Controls.Add($label6)
    }
}
})

####### Benutzer löschen Button

$button2 = New-Object system.windows.Forms.Button
$button2.Text = "Benutzer löschen"
$button2.Width = 147
$button2.Height = 32
$button2.location = new-object system.drawing.point(314,44)
$button2.Font = "Microsoft Sans Serif,10"
$Form.controls.Add($button2)       
###### Benutzer sehen Button       
$button3 = New-Object system.windows.Forms.Button
$button3.Text = "Benutzer sehen"
$button3.Width = 147
$button3.Height = 32
$button3.location = new-object system.drawing.point(75,94)
$button3.Font = "Microsoft Sans Serif,10"
$Form.controls.Add($button3)  

###### Exit Button
$button4 = New-Object system.windows.Forms.Button
$button4.Text = "Exit"
$button4.Width = 147
$button4.Height = 32
$button4.location = new-object system.drawing.point(313,93)
$button4.Font = "Microsoft Sans Serif,10"
$Form.controls.Add($button4)
$button4.Add_Click({
    $form.Close()
})


#### damit das GUI angezeigt wird.
 [void]$Form.ShowDialog()

 $Form.Dispose()