RH6 samba 3.5.10 @group not working

The problem I'm having is that if I spec a user id (valid user) in the share, I don't get prompted for a password when trying to access it from a Windows host. If however in the share options I spec a group name (ie. valid user = @aiswf), I get prompted for an account and password. The user accounts and groups have been created on the samba server. We joined the Windows AD domain (net rpc.)

Why is a group share access behaving differently from a user share access? Am I missing a config/setup step ?

Below is my smb.conf

[global] 

workgroup = DEVENG 

server string = %h Samba File Server %v 

hosts allow = 127. 10. 172. 

smb ports = 139 445 

# Domain Members Options 

security = domain         encrypt 

passwords = yes 

passdb backend = tdbsam 

password server = * 

domain master = no 

wins server = 10.XXX.XX.XX,172.XX.XX.XXX 

dns proxy = yes 

deadtime = 10 

# Browser Control Options
local master = no 

preferred master = no 

os level = 33 

# Filesystem Options
map archive = no 

map hidden = no         m
ap read only = no 

map system = no 

store dos attributes = yes
         hide dot files = no 



#=== Share Definitions === 

[neteng] 

comment = Network Engineering Share 

path = /fs_neteng 

browseable = yes 

writable = yes 

valid users = @neteng dignarn 



[aiswf]
comment = AIS Workflow Share 

path = /fs_aiswf 

browseable = yes 

writable = yes 

guest ok = yes 

admin users = arnoldr 

valid users = @aiswf