CCISS devices have paths (eg. "/dev/cciss/c0d0p1") which libguestfs didn't understand.
When virt-p2v converted a physical machine that uses CCISS devices to run in a VM, libguestfs inspection would fail because it didn't understand the /etc/fstab file containing these paths.
libguestfs has been updated so that it understands /dev/cciss/* paths appearing in guest /etc/fstab.
virt-p2v is now able to successfully convert these guests.