I installed samba server as part of the Ubuntu 10.10 distro. Couldn't make it work. The samba log for the connection would display the error:
smbd/map_username.c:140(map_username) can't open username map /etc/samaba/smbusers. Error No such file or directory.
The path is misspelled in the default smb.conf file. Fixing the path fixes samba.
Did you perhaps still have an old smb.conf file present when you installed Samba ? The default smb.conf file doesn't seem to set the username map at all.
Since this is a distribution-specific (not upstream) issue, please open a bug on Launchpad if you can reproduce it on a clean 10.10 install. Thanks.