Please help me ! "Selected Mac OS X installer is incomplete"

Hey everyone, when i try to create my bootable usb drive with unibeast and i select the OS, i have "Selected Mac OS X installer is incomplete" and "Your selected Mac OS X installer is the partial installer and doesn't contain everything that Unibeast needs to work correctly". What do i need to do ?

Thanks

PS: I'm doing this with a VM in Vmware