My configure line was the following: ./configure --enable-cgibindir=/var/apache/cgi-bin --enable-maxpopusers=unlimited --enable-vpopmaildir=/var/vpopmail --enable-htmldir=/var/apache/htdocs --enable-autoresponder-bin=/usr/local/bin/autorespond
I took out the --enable-maxpopusers and it has compiled fine.
