samba - Sep 2013 - Unpredictable behaviour of several network shares

Hello,
I have recently started having problems with my installation of Samba 
that I can't attribute to any single cause. On some of the computers I 
have networked (like 2-3 of total 40) sometimes I can't access some 
shares (again, 2-3 shares from 26 total). When this error occurs, 
Windows client tells me I might not have proper privileges but I can 
access the same share with the same network login/password from 
different computer or another login from that very computer. This mostly 
happens when computer is newly turned on or rebooted and dissappears 
after a while (15-30 minutes). It is possible to reproduce it by 
rebooting one of the affected client computers (not anymore 100% sure). 
Sometimes the shares work but windows machine keeps asking for 
name&password whenever you try to open folder or a file.
I'm not very skilled in samba (or linux) administration but I have root 
access to the server and will try to include info I find useful:
My server is running
/openSUSE 11.2 (x86_64)//
//VERSION = 11.2/
Samba is 3.4.3-3.8.1 (according to yast2)
Global configuration is as follows:
[global]
     workgroup = CENTRUM
     passdb backend = tdbsam
     printing = cups
     printcap name = cups
     printcap cache time = 750
     cups options = raw
     map to guest = Bad User
     include = /etc/samba/dhcp.conf
     logon path = \\%L\profiles\.msprofile
     logon home = \\%L\%U\.9xprofile
     logon drive = P:
     usershare allow guests = Yes
     add machine script = /usr/sbin/useradd  -c Machine -d 
/var/lib/nobody -s /bin/false %m$
     domain logons = No
     domain master = No
     local master = Yes
     os level = 65
     preferred master = Yes
     security = user
     wins support = Yes
     name resolve order = wins lmhosts hosts bcast
     unix extensions = No
     follow symlinks = Yes
     wide links = Yes
         log file = /etc/samba/samba-log.%m
     log level = 3
     map untrusted to domain = Yes


The problematic share (maybe it's not the most problematic but it's 
definitely most used):
[recepce]
     inherit acls = Yes
     path = /srv/recepce
     read only = No
     create mask = 0660
     directory mask = 0770
     force group = zamestnanci
     msdfs root = Yes

(last line added after problems started as per some solution I found not 
being really solution after all)

And I managed to get an error message that appears when the share is not 
accessible. The log is available here (I link it because of size and I 
didn't want to trim it as I don't exactly know what's important).

Is there anyone who can help? Is more info needed?
Thanks
-- 
Jan Odv??ka
<http://www.crsp.cz/>