Since I may not always be on the same machine or with the same operating system when I want to run a virtual machine I bring with me, I store them on a Western Digital MyPassport USB Drive.  This drive is formatted using the NTFS file system.  I had a problem when I first tried to run one using VMWare Server on Ubuntu 8.04.  The virtual machine would not start and it didn’t gave me an error.  Fortunately I found this blog post (Lornajane) that talked about a setting to put in the vmx file of the virtual machine:

mainMem.useNamedFile=”FALSE”

This worked perfectly for me too