[Samba] smb + nfs lock problem

[Jehan PROCACCIA]

Hello,
whenever I try to copy a new file from windowsXP (2K also) to a samba 
share which is NFS mounted on the samba server, I get an error on the 
client: "impossible to copy file.txt: the process cannot access the file 
because an other process has locked a part of it" (my english 
translation of the french message I have !)
It worked fine before (3weeks ago) and I think that problem appeared 
when I upgraded my NFS server, because the samba server running directly 
on that NFS server work fine (no lock pb) ,

I tried looking through samba locking mechanisms, but I'am a bit lost in 
there:
http://samba.org/samba/docs/man/Samba-HOWTO-Collection/locking.html
I blindly tested

[homes]
veto oplock files = /filename.htm/*.txt/
or
[global]
kernel oplocks = yes

with no success !
Do you have an idea ? is it a samba problem ? an NFS problem ? a windows 
client problem ?
I've got undred of users "locked" :-(
Thanks .


PS:

Here's my samba server system config:
bash-3.00# cat /etc/redhat-release
Fedora Core release 4 (Stentz)
bash-3.00# rpm -qa | grep samba
samba-common-3.0.23a-1.fc4.1
samba-client-3.0.23a-1.fc4.1
samba-3.0.23a-1.fc4.1
bash-3.00# uname -a
Linux fpublic.int-evry.fr 2.6.17-1.2147_FC4.vs2.0.2.2 #1 Thu Sep 14 
22:30:50 EDT 2006 i686 i686 i386 GNU/Linux

here's the NFS server config on wich samba works fine (local disk access !)

$ cat /etc/redhat-release
Red Hat Enterprise Linux ES release 4 (Nahant Update 4)
nfs-utils-1.0.6-70.EL4
system-config-nfs-1.2.8-1
nfs-utils-lib-1.0.6-3
samba-common-3.0.10-1.4E.9
system-config-samba-1.2.21-1
samba-3.0.10-1.4E.9
samba-client-3.0.10-1.4E.9