Tonight I'm doing some imaging of HP tablets and upgrading them from Windows XP to Windows 7. This is a new FOG installation and I just ran into this error. Here's the fix:
No matter what you named the FOG server on your network, make sure you have a DNS entry on your DNS server that DHCP is pointing to and create an A record named "fogserver" minus the quotes of course.
Once you do that then restart the machine you want to push the image of to your FOG server. Problem solved and it will upload after that. On a 100M switch you can expect about 1.4 to 1.5G/min so the average new image runs about 20-25 minutes to upload. Obviously gig switches are much faster provided your backend can keep up.