So this is what worked for me as a workaround. Hope this can help anyone else out.
I had to create the VMware folder under C:\Windows\Temp and copy our postsync script (postsync.cmd) into this location (C:\Windows\Temp\VMware). Once the script was there the desktop build completed successfully. To add I kept the desktop pool Guest Customization post sync setting pointed to c:\postsync.cmd (although I'm guessing I could have just pointed directly to Windows\Temp\VMware).
Seems like a bug to me where it's not moving the script to C:\Windows\Temp\VMware as it has done previously.
