The cause was a change in samba between versions 3.3.2 and 3.4.0.
It concern passwd backend. The symptoms was that Windows client prompted for password again after entering the correct username and password.
testparm did not report any errors for smb.conf file. In log files there were errors of that kind:
check_sam_security: Couldn't find user xxx in passdb.
When trying to mount the drive via command prompt, I get that error message:
System error 1326 has occurred.
The workaround is add this line in global section in smb.conf file:
passdb backend = smbpasswd
The issue is described more detailed in this page.
I suppose the other approach for solving the issue is to recreate the passwd file from the strach accourding the new tutorials.
Is this useful for you? Please comment.