They probably overtightened them then...damaging the face seal. You may have problems with the others in the future They only need to be a good "snug" to seal properly.
Yeah I am familiar with that, I get calls occasionally from friends that know I plumbed my whole house. And they will have a leak they can't get to stop, it is almost always a compression fitting that they have cranked down so hard on I can see brass shaving once i get it apart. Hand tighten then half a turn people its not a hard concept.
Kenny what do you think of these
http://www.gen-aircraft-hardware.com/template.asp?pagename=flrsav