Can't add apps/widgets to Nova launcher homescreen

Hi

I've just done a factory reset on my htc One. Htc backup failed miserably so I'm trying to manually reinstate my apps on Nova Launcher Prime. Long press and hold results in a popup of my homescreens in the background with no option to add apps or widgets. I've uninstalled/reinstalled Nova and checked the homescreen is unlocked but am pretty much out of ideas otherwise.

Any thoughts out there?

Thanks