Yesterday (July 18th 2016), CCLI updated the SongSelect web site. From what we can determine, SongSelect no longer offers songs in the USR format that Harmony imports. We have attempted to reach our CCLI contacts to determine a path forward but as for now SongSelect importing does not work in Harmony.
Importing from SongSelect is considered a major feature in Harmony and we will work towards a solution. This post will be updated as new information becomes available.
UPDATE August 1st 2016: Harmony 3.1.10 has been released to direct customers and submitted to the Mac App Store. It restores use of SongSelect.