I have been unable to add anything new to "Libraries" since PS Ver. 21 or 22. This has been an ongoing problem for almost 3 years and I have tried your suggested solutions with deleting CC Libraries in Application Support/Adobe, CEP Extensions, etc. over that time period to no avail. I've been using Photoshop since Ver. 3.0 (1994 or so) and can't recall a bug like this going this long without it being fixed. I can use the assets that are currently there but are unable to add any new ones. I am using 84.9 Mb of my 20 Gb storage, so I don't think a lack of storage is the problem. Your CC Installer still shows up as corrupt for the last 3 years and the Package Contents method doesn't work either - why hasn't this been fixed?
I've tried deleting libraries, creating new libraries, reinstalled countless times to no avail. This "Libraries" function or capability is useless to me in its present state.