[Samba] Problems with Windows Vista and Linux Samba share

[Per Dalgas Jakobsen]

Hi

I've set up a Debian machine with Samba 3.5.6, acting as a stand-alone 
server (NAS).
I have a Windows Vista client participating in a company domain, but the 
client should have access to the Samba (which is not on the domain).

I can connect from the Windows client to the Samba server using the 
servers IP-address.
I can immediately browse around, open and creating files and directories.
Then after a minute or so, Windows cannot use or reconnect to the share 
anymore...
I have to delete the connection "net use z: /delete" and then make a new 
connection.

/etc/samba/smb.conf:
---
[global]
     workgroup = XYZ
     netbios name = XYZ-NAS
     server string = %h server (Samba %v)
     log file = /var/log/samba/log.%m
     max log size = 1000
     syslog = 0
     encrypt passwords = yes
[data]
     comment = Our data
     path = /data/
     browseable = yes
     writable = yes
     valid users = abc
     public = no
---

Any suggestion as to what I am doing wrong?

What I really want to achieve; is to have my own little NAS attached 
physically to the company network, but not in any way participating in, 
or disturbing that network - I do not want to anger the IT department.
Only one user should get access to the NAS.

I hope someone can help me out...

~Per