No calendar showing on Rooms bookable unit - when clicking manage availability
Rooms and BAT are separate modules, you should fully un-install BAT and then follow the Rooms installation instructions. Rooms depends on the fullcalendar library, but not the full calendar module. 


  Within the Rooms module there is a rooms.make file which will download the library if using Drush or you can visit https://github.com/arshaw/fullcalendar/releases/download/v2.6.1/fullcalendar-2.6.1.zip to download it. The FullCalendar library should be placed in sites/all/libraries so that you end up with the file located here: sites/all/libraries/fullcalendar/fullcalendar.js


(quoted from http://docs.roomify.us/rooms/installation.html)