Sounds like the XML file is missing some information in it. I have seen similar things when trying to move VMs from a P2V using a third party utility. I ended up using the VCenter Standalone Converter.
Sorry I actually wrote about the whole project extensively on my blog. The short answer is I used various versions of the vCenter converter, in certain situations I installed the vCenter converter on the VM in order to convert it.
Iopoetve is correct. He let the VCenter Converter treat the VM as a physical pc. The converter created the VM vmdk, vmx file, etc. just like importing an OVA file would.