Hmm, in this case I don't know what is going wrong.
Look at that KB in order to be able to log in the helper after the conversion fails (actually you can log after it boots, no need to wait for the whole timeout): http://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=1036746
After you log in, try ssh to the source machine, inspect the network configuration, try ping etc.
BTW the helper log is /var/log/vmware-converter/vmware-converter-helper.log
HTH
Plamen