Samba shared file attributes changed by windows

Question

we set up a samba file server in our office and everything seems to be fine until one day. The server holds some MS Excel files on the server for everyone to access, all stations are either Windows XP or Windows 7

One windows station in particular keeps changing the attributes of only one file and sets a red only attribute to it. I searched all over the internet and I don't know what to do to fix this problem.

My Samba config is as follows:

#======================= Global Settings =======================

[global]
    workgroup = COTTONTEXDOM
    netbios name = grafubu
    server string = %h server (Server)
;   wins support = no
;       wins server = w.x.y.z
    dns proxy = no
;       name resolve order = lmhosts host wins bcast
    usershare allow guests = yes

#### Debugging/Accounting ####

    log file = /var/log/samba/log.%m
    max log size = 1000
;   syslog only = no
    syslog = 0
    panic action = /usr/share/samba/panic-action %d

####### Authentication #######

    security = share
;   workgroup = cottontexdom
    null password = yes
    encrypt passwords = true
    passdb backend = tdbsam guest
    obey pam restrictions = yes
    guest account = nobody
    invalid users = root
;   unix password sync = no
    passwd program = /usr/bin/passwd %u
    passwd chat = *Enter\snew\sUNIX\spassword:* %n\n *Retype\snew\sUNIX\spassword:* %n\n .
;   pam password change = no


########## Printing ##########

;   load printers = yes

;       printing = bsd
;       printcap name = /etc/printcap

;   printing = cups
;       printcap name = cups

;       printer admin = @ntadmin


######## File sharing ########

;   preserve case = yes
;   short preserve case = yes


############ Misc ############

;       include = /home/samba/etc/smb.conf.%m

;   socket options = TCP_NODELAY

;       message command = /bin/sh -c '/usr/bin/linpopup "%f" "%m" %s; rm %s' &

;   domain master = auto

;   idmap uid = 10000-20000
;   idmap gid = 10000-20000
;   template shell = /bin/bash

#======================= Share Definitions =======================

#[homes]
#   comment = Home Directories
#   browseable = yes
#   writable = yes
#   create mask = 0700
#   directory mask = 0700
;[netlogon]
;   comment = Network Logon Service
;   path = /home/samba/netlogon
;   guest ok = yes
;   writable = no
;   share modes = no

#[printers]
#   comment = All Printers
#   browseable = no
#   path = /tmp
#   printable = yes
#   public = no
#   writable = no
#   create mode = 0700

#[print$]
#   comment = Printer Drivers
#   path = /var/lib/samba/printers
#   browseable = yes
#   read only = yes
#   guest ok = no
#;   write list = root, @ntadmin

[c]
    path = /media/c_grafica
    comment =
    security = share 
    guest ok = yes
;   read only = no
    browseable = yes
    writeable = yes
    create mask = 0777
    directory mask = 0777
    force user = nobody
    force group = nogroup

[f]
    path = /media/f_grafica
    comment = 
    security = share
    guest ok = yes
    browsable = yes
    writable = yes
    create mask = 0777
    directory mask = 0777
    force user = nobody
    force group = nogroup

[registru_ordine]
    path = /home/david/Registru ordine
;   comment = 
    security = share
    public = yes
;   browsable = yes
    writable = yes
    create mask = 0777
    directory mask = 0777
    force user = nobody
    force group = nogroup

[dim_buz]
    path = /home/david/Dimensiuni Buzunare
;   comment =
    security = share 
    guest ok = yes
    browseable = yes
    writeable = yes
    read only = no
    create mask = 0777
    directory mask = 0777
    force user = nobody
    force group = nogroup

[switchfolder]
    path = /home/david/SwitchFolder
    write list = *
    store dos attributes = Yes
    security = share 
    guest ok = yes
    browseable = yes
    writeable = yes
    create mask = 0775
    directory mask = 0755
    force user = nobody
    force group = nogroup

Can someone please tell me what I am doing wrong?