Sorry for not getting back to you sooner (two weeks of vacation, you know).
Thank you agauvrit, your solution seems to work!
The test machine successfully installs the agent via GPO at startup (it takes 1 or 2 minutes). The solution was indeed to apply the GPO only to an OU containing THAT computers (You must delete or move everything else, user accounts etc...).Create an Organizational Unit (OU) and move the WAPT deployment test workstations into it.
This OU contains only computer accounts, no users (which are usually in CN=Computers), and apply the Group Policy Object (GPO) to these computers.
Thanks again, all that's left is to put it into production!
