I'm having the same issue. I tried three times on my MacbookAir to convert an XP laptop to a VM.
I finally ended up connecting a crossover cable between them and it still failed. Firewalls off, static IP, simplest setup ever.
Gave up and brought my old XP laptop to work.
Tried with both a MacbookPro and my coworkers iMac.
Both fail after the code, after user auth, after free space confirmation and say "Windows is having trouble talking to your Mac. Try turning off System Preferences -> Sharing -> File Sharing and starting again. If you've enabled a firewall, disable it while migrating your PC."
Now, I've done and done and re-done the above a gazillion times, and this error message is a POS.. But it can be inferred that either something on the MAC or something on the PC is disallowing the program running on the PC from talking how it needs to to the program on the MAC.
So I fired up Wireshark and captured packets.
Everything works fine up until you get to the point where it's calculating time remaining.
Then the PC being migrated tries to contact the MAC on port 80. I've nmap'd the device, done a netstat, and cannot find anything running on the mac listening on port 80 that the PC would ever be able to talk to or connect to. So the MAC does what it is supposed to, and sends an RST ACK back to the PC.
This happens three times, then the process fails with the above message.
it is obvious that the "Migrate Existing PC" functionality of VMWare Fusion 4 is broken on Mountain Lion 10.8
Someone needs to fix this.
I've uploaded a PCAP and this screenshot to an open issue I created that is at SRCN#13310127504
