[ovirt-users] VM-Pool is already attached to a User

I created a VM pool (20 Windows) and the first 6 users took a virtual machine in the VM portal. the following other users have this message "Cannot attach VM to VM-Pool. VM-Pool is already attached to a User" I have 15 users and 20 VMs available, do you know why I have this message ? I have no user registered in the permissions tab of the vm available. ovirt 4.4.1 Thank you.