These are the manual steps needed to create an image based lighting setup that is compatible with HDR Light Studio.
When HDR Light Studio creates an IBL Hook for you, it generates this setup.
Select Environment... in the Rendering menu
Click on the None button to assign an Environment Map image file
Choose Bitmap and press OK
Then select a HDR or EXR standin file and press Open
Press OK on the following dialog.
HDR Light Studio will now see and connect to this IBL setup.