Warning, make a backup of /tftpboot/pxelinux.cfg/default before doing any of this. It will replace without prompting, wiping out any custom ISOs.
With Fog 0.32 if you attempt to use Quick Image, you will be prompted for a password. Log in to the management interface, Other Information, PXE BootMenu to create the PXE Menu and set the fog.quickimage password. Make sure to use a password 4 chars or longer.
PXE Menu: http://X.X.X.X/fog/management/index.php?node=about&sub=pxemenu
After you get past that point, you'll encounter: "Enter a valid FOG username and password"
Your normal user/pass may fail silently if the password is less than 3 characters, for instance 'fog'. Log into management interface, User Management, click the user (fog) and set a password 4 chars or longer.
Users: http://X.X.X.X/fog/management/index.php?node=users