Cutout from logfile:

12293 [2008/02/26 00:27:55, 5] auth/auth_util.c:debug_nt_user_token(448)
12294   NT user token: (NULL)
12295 [2008/02/26 00:27:55, 5] auth/auth_util.c:debug_unix_user_token(474)
12296   UNIX token of user 0
12297   Primary group is 0 and contains 0 supplementary groups
12298 [2008/02/26 00:27:55, 3] smbd/sec_ctx.c:pop_sec_ctx(339)
12299   pop_sec_ctx (0, 0) - sec_ctx_stack_ndx = 0
12300 [2008/02/26 00:27:55, 10] passdb/lookup_sid.c:lookup_name(64)
12301   lookup_name: Unix User\ladanyi => Unix User (domain), ladanyi (name)
12302 [2008/02/26 00:27:55, 10] lib/util_pw.c:getpwnam_alloc(76)
12303   Got ladanyi from pwnam_cache
12304 [2008/02/26 00:27:55, 10] smbd/share_access.c:user_ok_token(208)
12305   User IPR-OFFICE/ladanyi not in 'valid users'