samba - Oct 2005 - samba errors: (87) The parameter is incorrect. (1326) Logon failure: unknown user name or bad password.

I get these repeated errors from my windows server but cannot
understand why. I am running samba on fedora 4 boxes and my servers run
on windows 2000. Whenever someone attempts to manually access a shared
volume on a linux box and use the right credentials we never experience
the 1326 error. I included the samba config file below and more details
of both errors from event viewer.
Does anyone have a clue why both errors occur like dozens of times
daily? We are using samba 3.0.14 and the error appears more frequently with
more load.

Error messages on the Windows servers:

(87) The parameter is incorrect.

or

(1326) Logon failure: unknown user name or bad password.

smb.conf file:

#======================= Global Settings
====================================
[global]

workgroup = WORKGROUP

server string = Server

log level = 0

log file = /var/log/samba/log.%m

max log size = 50

security = user

encrypt passwords = yes

smb passwd file = /etc/samba/smbpasswd

socket options = TCP_NODELAY SO_RCVBUF=8192 SO_SNDBUF=8192

local master = no

dns proxy = no

syslog only = yes

#============================ Share Definitions
=============================
[sharea$]

path = /a

writeable = no

write list = @group

create mask = 775

[shareb$]

path = /b

writeable = no

write list = @group

create mask = 775

[sharec$]

path = /c

writeable = no

write list= @group

create mask = 775