Program Crash on Startup

[Imoddedu]

This program I made crashes on startup, I do not know what I am doing wrong, can anybody help me?
Here is the code-

Public Class Form1

    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        Timer1.Enabled = True
    End Sub

    Private Sub Timer1_Tick(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Timer1.Tick
        AppActivate("Chat Window")
        Do
            SendKeys.Send(TextBox1.Text)
            SendKeys.Send((Chr(13)))
        Loop
    End Sub
End Class