Dear Drew Reece,
Thanks for the information.
But I was already aware of this article.
As I pointed out: I can log into the shared folder on my ubuntu machine from my mac. But the other way round does not work. There are rather strange issues.
When I tried to connect from the cli, I got the following answer:
[code]$ smbclient -L MacBook-Air-van-Marc.local
WARNING: The "syslog" option is deprecated
Enter marc's password:
session setup failed: NT_STATUS_LOGON_FAILURE[/code]
So: my ubuntu cant log in. That's clear enough.
Nevertheless it can [b]contact[/b] the mac, as the "nmblookup" command shows:
[code]$ nmblookup -AS 192.168.x.xxx
Looking up status of 192.168.x.xxx
MACBOOKAIR-Dxxx <00> - H <ACTIVE>
MACBOOKAIR-Dxxx <20> - H <ACTIVE>
WORKGROUP <00> - <GROUP> H <ACTIVE>
MAC Address = <een aantal letters en cijfers>[/code]
So: why is there that: "NT_STATUS_LOGON_FAILURE"??
On the graphical plain: when I use the gui in "nautilus" (graphical file-manager in ubuntu)to log in, I get this window:

I get the choice of login in as a registered user, with password, or "anonymously", without password.
Neither works! The login window disappears and reappears endlessly!
I do not know is the developers are aware of this issue?
It does not ruin my life! I installed SSH/SFTP protocol and that works perfectly in both directions between mac and ubuntu. But I want to solve this strange samba-puzzle. Or at least find out what causes it.
Thanks for your patience and attention.
Marc.