It seems that version 2.6 introduced a problem whereby the program will not launch if you are logged in as a non-administrator user. In version 2.51, you could get around this by placing a copy of the app in the user's home directory and using that one, but that doesn't work with 2.6.
A pity. This is a great program otherwise.
MacPAR deLuxe
Create and process PAR/PAR2 files and unpack RAR archives.
Version: 3.8