Strange problems, is it the lvm?

Hi,
I've created a 680gb volume group with reiserfs on top of lvm, which is used frequently by users. it worked fine for two weeks and now I have that strange problem:

root@main:~# ls /users
/usr/bin/ls: /users/Hell: Permission denied
/usr/bin/ls: /users/Blade: Permission denied
/usr/bin/ls: /users/Ferdy: Permission denied
...
Seems like a fs corruption to me. I fixed that with reiserfsck --rebuid-tree. The system worked fine again for a few days and the problem appeared again. My configuration is Slackware 9.1 updated to current, linux kernel 2.6.4.
 LVM version:     2.00.08 (2003-11-14)
 Library version: 1.00.07-ioctl (2003-11-21)
 Driver version:  4.0.0

IMHO the problem is in the lvm or the combination lvm + reiserfs? Perhaps my lvm version is old or i need some patches to the linux kernel? Do you have any idea what is the problem here? Any suggestions?

P.S. Please apologize me if you find that post a bit offtopic but I'm despaired.