Win32 FindWindow()

Hi!
I'm haveing trouble getting some of the Win32 functions working in Max and am wondering if someone can help me out. Ive added the following to user32.bmx in win32.mod:

Function FindWindow( lpClassName:Byte Ptr,lpWindowName:Byte Ptr ) = "FindWindowA@8"

I've built win32.mod (debug and release) and running the following code:

class:String="Calculator"
title:String="SciCalc"
hWnd=FindWindow(class.ToCString(),title.ToCString())

Print hWnd

With windows calculator running I get 0 for the handle. Any ideas on what I'm doing wrong?