[Samba] oplock windows XP client

[Marc Chachereau]

Hi,
I use samba for 5 years in a small enterprise network. We have recently 
changed our windows client and migrate from windows 95 to windows XP :-).
Samba is running on a debian woody. Since we are using windows XP home 
edition I can see the following log messages  : 

[2004/04/02 15:27:50, 0] smbd/oplock.c:oplock_break(758)
  oplock_break: receive_smb error (Success)
  oplock_break failed for file POSITION CONTRATS GRANEA/Contrats et 
PAF.xls (dev
 = 303, inode = 426012, file_id = 166).
[2004/04/02 15:27:50, 0] smbd/oplock.c:oplock_break(843)
  oplock_break: client failure in break - shutting down this smbd.

I don't know what an oplock is and I need your help to solve this problem.
Thank you