@bigpup, Thank you for your suggestions. I tried some of your methods and did more investigations. Did find some interesting clues. I actually met two issues with the same error information which are shoed in the earlier post. I am using GRUB as the boot loader and config the menu.lst file. 1. Fruga...

Download ISO image to usb flash then start up the computer from usb flash. Could enter the 1st menu of Xenialpup. Then choose an option. It showes to load Xenial pup linx but it will fail. The error log shows can not find the puppy_xenialpup64_7.5.sfs. Error is too critical, dropping out to conole.....