Ubuntu shares via nautilus are read-only

The problem :

The folders shared with nautilus are read-only, no matter what options you choose in the folder sharing dialog. The setting are ok.
Here is a dump of net usershare info --long

[share]
path=/home/user/share
comment=
usershare_acl=Everyone:R,USER\(null):F,
guest_ok=n

Even with guest acces and the folder permissions set to drwxrwxrwx it still doesn't work.

The Solution :

Adding force user = user in the [global] section of /etc/samba/smb.conf solves this issue. Puting security = share also solves the win2000 access denied.