Thank you for your rapid reply.
Seems to me that ut should be "uid" and not
"cn" here according to
what you found in your LDAP server.
I've tried "uid" in this part before, but it didn't help. Changed
xwiki.cfg to:
xwiki.authentication.ldap.bind_DN=uid={0},ou=People,dc=debuntu,dc=local
xwiki.authentication.ldap.UID_attr=uid
Checked now again - unfortunately, result is the same.
Patricia