virtualbox.org

I am afraid I have no clue either. Never dealt with Windows programming stuff, never wanted to
You should definitly go on the dev mailing list for this I think.

Hi HenryHux,
It sounds like you may be compiling an x86 version of your application to use on a 64-bit version of Windows - this won't work; you'll need to build as a native x64 application to interface with VirtualBox.