You are using a pre v0.19 version of SystemImager. Please download the latest version from http://systemimager.org/.
If you must use a pre v0.19 version for some reason, be sure that your kernel has "ramdisk" support or that you have ramdisk support with a module. If you are using a module, be sure that it is loaded with the modprobe command; however it's probably easier to get the latest version.