Sending messages

[Dave]

Hi,
I am sending windoew message from a c# application to c++(unmanage)
application using this code
System.UInt32 rm= RegisterWindowMessage("12345");

System.IntPtr ptr=(IntPtr)HWND_BROADCAST;

PostMessage(ptr,(int)rm,5,5);

PostMessage(ptr,WM_AAA,5,5);

but the c++(vc-6 mfc) dont catch the message, when i use the
RegisterWindowMessage("12345"); in the c++ application it return a diffrent
number from that in the c# application why?

Thanks.