Owing to help a lot people at this discussion list I solved most of my problem with LTSP 5.4.5-23.
Remains only one at this moment.
I restored my older thin client image (Scintific Linux 6.1 i386). Thin client boots, I can use Windows with xfreerdp and rdesktop packages, but I can't log in to the system via LDM.
I executed ltsp-update-sshkes (with -u parameter too) but with no result.
Could anybody support me with this problem?