Problem solved: A directory in the path to the source code had a space in the name.
From: c0d3g33k <firstname.lastname@example.org>
Sent: Mon, January 31, 2011 11:12:12 PM
Subject: Re: [Fwknop-discuss] Compile on 64-bit?
fwknop compiles fine on 64-bit. Seems like you need to do a bit more troubleshooting.