if the host records already exist, you may have to go back to each record and select the “Active Directory” menu option, and choose to join the computer to the domain after the image task. I had this issue because I had host records created before I had the Active Directory credentials working properly.
Make sure the account you are using is specifying the FOG_AD_DEFAULT_DOMAINNAME as a FQDN (something.something.etc), your FOG_AD_DEFAULT_USER is specified as (DOMAIN\User), and your FOG_AD_DEFAULT_PASSWORD has been FOGCrypted properly. I have not had success is specifying the FOG_AD_DEFAULT_OU just yet, but I plan to work through that next. For now, they are joined to the default Computers location, and I move them to the correct OU as part of the deployment.
You need Account Administrators group membership in AD, OR be a domain admin, OR be delegated computer account management rights on the default Computers location and any other locations you plan to put machine accounts.