Might just be a 'permissions' issue or the like - you can repair them in disk utility, or use Applejack, which is my preferred occasional Mac repair routine - works a treat, very easy. Worth giving these a try first...
Applejack here:-
http://applejack.sourceforge.net/
(here's a review of it, if the name sounds slightly worrying ;-) -
http://download.cnet.com/AppleJack/3...4_4-40293.html )