[Samba] password revalidation samba

[Joshua]

Hello,

I recently upgraded my server from samba 2.2 to Samba 3.0.14a. Samba is
running as PDC. Now i got a strange thing when someone tries to access a
share for which (s)he is not authorised, a popup box shows up on the W2K
client asking for name and password again, while this used to be a popup
box with the announcement that the user is not authorised to access the
share.

Why is this popup box showing up now?
Im using tdbsam as backend, security = user
and for example a share defined as:
[system]
	comment = System Config Files
	path = /etc
	invalid users = @users
	write list = @admin
	read only = No

users in the unix group users get the popup box.