"open" does not work (for xz file)

I needed to extract a .tar.xz file, so I started RAR Extractor Star and pulled down "FIle" -> "Open...". I browsed to the right directory and saw the .tar.xz file, but it was grey and could not be selected.

Fortunately, I was able to go into Finder and double-click the .tar.xz file. That brought up RAR Extractor Star, and I was able to extract.

Sford about RAR Extractor - Unarchiver Pro