You want to have a look in composer log file (for QuickPrep): C:\Windows\Temp\VMware\vmware-viewcomposer-ga-new.log

Make sure your OU is setup correctly for your pool, and the service account you have created for managing VMware desktops in the Horizon environment has permissions to create objects in that area.

Depending how you built the image, it's unlikely this is the issue, but this article may still be relevant: VMware Knowledge Base