Can't find the Knoppix filesystem error never disappear

[demonstrate]

I read a few introductions to remastering and customiztion, and I am just making my first Knoppix. But whenever I create the bootable iso file, and boot it in a virtual pc, it always responds to me an error:
Can't find the Knoppix filesystem
when the booting sequence comes to the end of scanning filesystem devices, such as /dev/hda1 and etc.

I thought it might be caused by an md5 sum error, and I searched here ending up with a command to refresh the md5sums in KNOPPIX directory:
rm KNOPPIX/md5sums; find -type f -not -name md5sums -not -name boot.cat -not -name isolinux.bin -exec rm {} \; > KNOPPIX/md5sums
because when I failed with my compressed_fs img I thought the image may be wrong, so I actually used all the file in the cd-rom to re-create a knoppix cd. I checked the original english version in the virtual pc and it can be booted correctly. But with my own it fails.

I thought about my way of creating the iso file. This is:
mkisofs -R -l -J -b boot/isolinux/isolinux.bin -c boot/isolinux/boot.cat -no-emul-boot -boot-load-size 4 -boot-info-table -o ../released/try.iso .

Any suggestion is fully appreciated! Thanks!