client frequently disconnect from my server Samba

[equipe web]

Hello !
I've got a problem with Samba and my network
I have a linux server with a Mandrake 7.2 Samba 2.0.7 and clients are Pc 
under Win98
Frequently my clients disconnet from my share ressource (about every 20 
minutes) and we had to restart samba and zindows to solve the problem ( 
sometimes it doesn't work at all).
In my smb.conf  i have turned security as user, commented all the server 
options (local master, domain master)
wins support is Yes.
In log.smb I read :
locking/shmem_sysv.c:sysv_shm_open(667)
Can't create or use IPC area. Error was Le fichier existe.
locking/locking.c:locking_init(174)
ERROR: Failed to initialise share modes

I tried to proceed the DIAGNOSIS.txt and it failed at the test 3 (but 
sometimes it worked)
smbclient -L zeus
added interface ip=192.168.1.1 bcast=192.168.1.255 nmask=255.255.255.0
Got a positive name query response from 127.0.0.1 (192.168.1.1)
read_socket_with_timeout: timeout read. read error = Relais brisé (pipe)
session request to ZEUS failed (code 0)

Could you help me please !
PS : sorry for my approximative English, it's not my native language.
Alexandre