To those having the same problems with download destination directory error:

I installed LimeWire under /opt/LimeWire and had that same error during the first-time configuration process...I believe the problem has something to do with permissions, so I installed it to my home directory under /home/<username>/LimeWire... everthing worked out fine. Sort of an easy fix, but not great if any other users would like to have access to the program.

I'm sure it has something to do with what your group permissions are, but I am not sure what 'group' to add myself and/or other users to in order for everyone to have access.

Not sure it that helps, but I'm sure it will give clues as to what the problem is for users who are more experienced with Linux.

Hope I helped, even in the slightest.