Error Getting Form Handler (Vb.net) - vb.net

Question

I have the current code:
Public Declare Function FindWindow Lib "user32.dll" Alias "FindWindowA" (ByVal lpClassName As String, ByVal lpWindowName As String) As Long
<DllImport("user32.dll", SetLastError:=True, CharSet:=CharSet.Auto)> _
Private Shared Function SendMessage(ByVal hWnd As HandleRef, ByVal Msg As UInteger, ByVal wParam As IntPtr, ByVal lParam As String) As IntPtr
End Function
Declare Auto Function SendMessage Lib "user32.dll" (ByVal hWnd As IntPtr, ByVal msg As Integer, ByVal wParam As IntPtr, ByVal lParam As IntPtr) As IntPtr
Public Function WindowHandle(ByVal sTitle As String) As Long
WindowHandle = FindWindow(vbNullString, sTitle)
End Function
Dim CurrentProcess As Process
Dim CurrentHandle As IntPtr
Private Sub Timer1_Tick(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Timer1.Tick
SendMessage(CurrentHandle, 256, Keys.A, 0)
SendMessage(CurrentHandle, 257, Keys.A, 65539)
End Sub
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
Try
CurrentProcess = Process.GetProcessesByName(ListBox1.SelectedItem.ToString.Remove(0, ListBox1.SelectedItem.ToString.IndexOf("{") + 1).Replace("}", ""))(0)
CurrentHandle = New IntPtr(WindowHandle(CurrentProcess.MainWindowTitle))
Timer1.Start()
Catch ex As Exception
MsgBox(ex.Message)
End Try
End Sub
If you take a look at the button sub, every time it runs, it errors with "Arithmetic overflow error!"
What is wrong here? This should work... right?
Sorry, this is a bit vague but it's as much as I know.

Answer 1

Your Declare statements are correct but the way you call them is not. The loose typing allowed by VB.NET is getting you in trouble, the kind you can't diagnose. The cure for that is letting the compiler tell you that you did it wrong. Put this at the top of your source code file:
Option Strict On