repetitive errors on user machines - DC migration from a windows XP based to a windows 7 based network

I'm not aware of any GPO settings that would cause your symptoms when applied to Windows 7 machines, vs Windows XP machines so I'm leaning more toward something with the image. All other components of your network should work fine with how you've described it.

To troubleshoot, I would start by wiping a machine and installing from scratch using the Windows 7 disk. Create a computer object in the Computers container in AD, so that only policies applied at the domain level are applied when you add it to the domain. If you still get the same issues after adding it to the domain, start looking at the what policies are applied at your domain level and the settings within those.

If you don't get the errors, then move the computer object in AD to where it should be, and where all GPOs necessary will be applied. After that, make sure you don't get the same errors. If you do, you could start investigating the settings in the other GPOs that got applied.

You could also report back with the event ids and sources of the errors on the workstations.