In Kolab 16.1 on Centos 7 with roundcubemail-1.2.3-3.1.el7.kolab_16.noarch, if in new calender event modal window you first go to Resources tab to book the resources and then to Participants, you can see that meeting doesn't have an organizer. If you first go to Participats tab, you can see the Organizer being set, then you can book the resource.
The absence of Organizer makes wallace fail to recognize resource book request. Such an invitation is passed along and bounce back to meeting creator with error "no such user 'resouce-confroom-Room1'".