the command for unrar-free is
unrar x your_archive.rar
Maybe you can try Ark by KDE in Synaptic.
This is another archive manager.
But it can be the dependancie you use to open it. Unar or unrar-free. I don't
think Ark or Archive Manager have something to do with it.
I had this probleme before.
I don't know why, unar and unrar-free are incompatible once both installed on
Trisquel 7.
Uninstall only unrar-free from the command line or synaptic. Then, have a try
with Archive manager. It should work.
This has worked for me...
