samba - Jun 2011 - Folder redirection and "guest user (from session setup) not permitted to access this share" in logs

Hello, sambadmins.

First some background.
Server is (soon to be dist-upgraded) Debian Lenny 64-bit and samba version
is 3.5.6~dfsg-3~bpo50+1.
Samba as PDC, LDAP as passdb backend, pam/nss uses same ldap on Linux side,
so all ID-s are "in sync".
Locks settings are default.
Windows XP SP3 as clients.

Few weeks ago I started to see following in logs:

[2011/06/08 15:17:51.766871,  2]
smbd/service.c:587(create_connection_server_info)
  guest user (from session setup) not permitted to access this share
(some.user)
[2011/06/08 15:17:51.766898,  1] smbd/service.c:678(make_connection_snum)
  create_connection_server_info failed: NT_STATUS_ACCESS_DENIED
[2011/06/08 15:17:51.774699,  2]
smbd/service.c:587(create_connection_server_info)
  guest user (from session setup) not permitted to access this share (
some.user)
[2011/06/08 15:17:51.774728,  1] smbd/service.c:678(make_connection_snum)
  create_connection_server_info failed: NT_STATUS_ACCESS_DENIED
[2011/06/08 15:17:57.268946,  2]
smbd/service.c:587(create_connection_server_info)
  guest user (from session setup) not permitted to access this share (
some.user)

I didn't turn much attention to it since I didn't hear anyone
complaining.
But today I got few worring letters and started to investigate.
Found out following:

When user tries to write to network drive (map network drive in windows) or
\\server\some.user share, everything is okay.
But!
We have Desktop and My Documents redirected to network drive and making new
files/folders to desktop and my documents fails
and logs will be filled with lines mentioned before. No error message from
Windows side, not even event logs - just files doesn't show up.
Editing existing files seems to okay. Testing with smbclient is ok.
Some PC-s can write new files after 1-2 second lag, but with same error in
logs.

Any ideas?

-- 
Sent from my PC.