sanboot -d switch

[robinsmidsrod]

The argument to -d (short for --drive) is the "BIOS drive number". The first traditional floppy is 0x00, the first HDD is 0x80 and the first CD-ROM is (I believe) 0xe0. To me it seems like the OS is not accepting the sort of method iPXE is using to provide the virtual drive via Int 13h. On the problematic machines you might have luck if you try to disable any other storage controllers enabled in the BIOS. This might make the utility unusable (because it is for the storage controllers), but at least it should tell you if that is your problem area or not.

You might also be running into the issue that sanboot provides a read-only virtual drive, while memdisk gives you a read-write virtual drive. Depending on your OS/utility that might make a difference.