Perhaps you have to change the security level of the SAMBA server.
Edit the /etc/samba/smb.conf file and change
security = user
to
security = share
or add this line to the [global] section, it it does not exist.
You also have to add the following line to that section:
encrypt passwords = yes
I also recommend to install KSambaPlugin
http://ksambakdeplugin.sourceforge.net/, for a graphical configuration.
Greetings,
Jan