After clicking the "Prepare for Synchronization" option for a target virtual machine in the Migrate Client, the "Configure..." button is grayed out.
View the virtual machine either with vSphere if the target container is an ESX server or with Hyper-V Manager if the target container is a Hyper-V server.
Locate the target virtual machine in question.
Configure the virtual network interface card so that it will connect at power on and save the change.
From within the Migrate Client, refresh the details of the target container that hosts the target virtual machine in question.
After the refresh job completes, try to configure the "Prepare for Synchronization" job again.
The virtual network interface card of the virtual machine needs to be configured to connect at power on before the "Prepare for Synchronization" job can be configured.