Problem with deleting files

Hi,

I'm currently experiencing a weird problem : some of my folders are 
completely empty (ls -a doesn't even mention . or ..)
But, I cannot remove them, and a ls is very very slow (but just in those 
folders, and it is quite rare, but now I cannot update firefox, nor 
openoffice, because make clean will fail).

uname -a gives :
FreeBSD *.fr 7.0-CURRENT FreeBSD 7.0-CURRENT #0: Fri Aug 26 10:12:03 
CEST 2005     root_at_*.fr:/usr/obj/usr/src/sys/MYKERNEL  i386

my questions are :
Is it Freebsd related, or may it be a problem with my hard disk ?
Is there a way to delete, or just unlink a folder, even if it doesn't 
appear to be empty ?

Currently, I'm trying to make world again, to see if the problem 
desappear, but I'm experiencing a problem with groff. By the way, is it 
possible to make world without groff ? Do I need it to make my system 
run well ?

Thanks
-- 
Gregory