When I click my Exit Program button, it says

Code:
Object reference not set to an instance of an object.
And sometimes I don't quite remember but it says something along the line of

RoundRobinPro is Disposed... (My Main app)

This is my login form, which I have made, the code I use is below

Code:
Option Strict On
Option Explicit On

Public Class LoginForm1
    Private Sub OK_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles LoginButton.Click
        Dim quit As Boolean = True
        If SignupRadio.Checked Then
            If System.IO.Directory.Exists("C:\Program Files\Round Robin Pro\Variables\" & _
            UsernameTextBox.Text) Then
                quit = False
            Else
                System.IO.Directory.CreateDirectory("C:\Program Files\Round Robin Pro\Variables\" & _
                UsernameTextBox.Text)
                RoundRobinPro.Dir.UsernameDir = RoundRobinPro.fnc _
                .CapitalizeString(UsernameTextBox.Text)
                MsgBox("Your account has been created", MsgBoxStyle.OkOnly)
            End If
        End If
        Dim errorString As String = ""
        If LoginRadio.Checked Then
            If Not UsernameTextBox.Text.Length > 4 Then
                quit = False
                errorString &= "Your username must be atleast 5 characters long." & ControlChars.NewLine
            End If
            If Not PasswordTextBox.Text.Length > 4 Then
                quit = False
                errorString &= "Your password must be atleast 5 characters long." & ControlChars.NewLine
            End If
            If Not ConfirmPw_t.Text.Length > 4 Then
                quit = False
                errorString &= "Your confirm password must be atleast 5 characters long." & _
                ControlChars.NewLine
            End If
        End If

        If quit Then
            Me.Close()
        Else
            MsgBox(errorString)
        End If
    End Sub

    Private Sub Cancel_Click(ByVal sender As System.Object, ByVal e As System.EventArgs)
        Me.Close()
    End Sub

    Private Sub Timer123_Tick(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Timer123.Tick
        If SignupRadio.Checked Then
            ConfirmPw_t.Visible = True
            ConfirmPw_l.Visible = True
            LoginButton.Text = "Signup"
        Else
            ConfirmPw_t.Visible = False
            ConfirmPw_l.Visible = False
            LoginButton.Text = "Login"
        End If
    End Sub

    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        Application.Exit()
    End Sub
End Class
Anyone know what's wrong?