samba - Oct 2002 - Strange windows error writing to samba share:

I've got a samba share that been up for a week with no trouble, but
suddenly my users are having write problems.

When copying a file using Windows Explorer, a 0-length file is created on
the share, then the following message is displayed on the client:

<dialog box>
-----------------------------------------------------------------------------------------------------------------------------
"This folder already contains a file named "<filename>" 
Would you like to
replace the existing file:

<icon> 0 bytes modified: <current time stamp>

with this one:

<icon> 19.3 MB modified: <in the past>
-----------------------------------------------------------------------------------------------------</dialog

box>

when the users click "ok", the following error is displayed:

Cannot copy <filename>: Access is denied.  The source file may be in use.


i've got debug levels set to 5, but i'm not seeing any errors in them.

Thanks!

system info:
OpenBSD 3.1-stable on a Sparc64 machine.
smb.conf:


$ cat /etc/samba/smb.conf
# This is the main Samba configuration file. You should read the
# smb.conf(5) manual page in order to understand the options listed
# here. Samba has a huge number of configurable options (perhaps too
# many!) most of which are not shown in this example
#
# Any line which starts with a ; (semi-colon) or a # (hash)
# is a comment and is ignored. In this example we will use a #
# for commentry and a ; for parts of the config file that you
# may wish to enable
#
# NOTE: Whenever you modify this file you should run the command
"testparm"
# to check that you have not many any basic syntactic errors.
#
#======================= Global Settings
====================================[global]
        remote announce = 162.70.219.21
        wins server = 162.70.219.21
        dns proxy = no
        security = user
        encrypt passwords = yes
        server string = Samba Server
        workgroup = MYGROUP
        socket options = TCP_NODELAY
        netbios name = cacssun5
        log level = 5
        log file = /var/log/smbd.%m
        load printers = no
        netbios aliases = sun5
        max log size = 50
        socket options = TCP_NODELAY


[software]
        path = /export/home/cm/software
        level2 oplocks = yes
        force directory mode         force create mode         fake oplocks =
yes
        force group         sync always = yes
        valid users         short preserve case = yes
        case sensitive = yes
        force user = cm
        strict locking = yes
        writeable = yes
        preserve case = yes
        map system = yes
        map hidden = yes
        delete readonly = yes
        mangle case = yes