[Samba] samba file rights. help

[Attila Soki]

hi,

i have a samba 2.2.5 on debian 2.4.19 (i386)
(under samba 2.2.4 occurs the same error)

my problem is the following:
sometimes occurs a very strange error. if i copy files from
windows 2000 or from windows xp to one of my shared drive,
the samba server removes all rights from the files.
it strores the file, sets the owner and group, but nobody has
read or write rights..

i think, this is a configuration error, but i can't find it.
please help.

thank you,

ati

ps: here is some more info

ls -l /home/blabla
drwxrws---   15 root     vertrieb     4096 Sep 13 14:25 vertrieb

here is the config of the service:
[vertrieb]
comment                 = Vertrieb public Ordner
path                    = /home/blabla/vertrieb
browseable              = yes
read only               = no
writeable               = yes
create mode             = 0660
force create mode       = 0660
security mask           = 0000

directory mode          = 0770
force directory mode    = 0770
directory security mask = 0000

force group             = vertrieb
valid users             = @vertrieb

case sensitive          = yes
preserve case           = yes
default case            = lower
guest ok                        = no
hide unreadable         = yes