In general those cases where customizations fail, it is usually for the same reasons customizations fail in vsphere when using the customization wizards to create a VM form a template. Things like proper communications (DNS, DHCP, NTP, HTTP/S, etc.) are needed for the vm customization to work.
Aside from the above mentioned, check the following:
SYSPREP tools on vCenter - these are needed for XP VMs.
DHCP must be used for the Win VMs.
Static IPv4 address must be used for TAF.
Check vCenter logs for errors on the customization failures.