What can prevent a successful migration with VMotion?

What can prevent a successful migration with VMotion?

A.
network cards located in different server slots

B.
a physical CD-ROM that is connected from the virtual machine

C.
different CPU clock speeds

D.
one of the virtual disks that is a mapped SAN LUN

Explanation:
VMware DRS and VMotion: Improve workload balance, prevent problems

Some virtual machines may fail to migrate, whether by automatic VMotion task or if evoked manually. This is generally caused by obsolete virtual machines, CD-ROM binding or other reasons that may not be intuitive