Iam new to redhat linux 6..when iam reboot the mechine i will getting an error message cold not update could not update iceauthority file /var/lib/gdm/.iceauthority and user login is not appearing can anybody please give me exact solution...its very important..

please use useful thread titles. What use is "help me"?? Also try a "please" or "thank you" in future too.

This is for ubuntu but seems reasonable advice. http://ubuntuforums.org/showthread.php?t=1763076 Check that you've not run out of disk space first though, and that the file isn't owned by gdm.

this is red hat RHEL6
A NOT free operating system
A OS that you MUST BUY a support contract for ( the standard is $ 299/ year )

if it is THAT important
ask your tech support that you paid for ( and paying every year for)
http://www.redhat.com/support/customer-portal.html
did you by chance turn off SELinux , then make changes , then turn on SELinux ???
or is /var on a different partition than the / and the rest of the os ?

reset the used group

boot into "single user" mode as root and run
or
boot in in RESCUE mode using the install dvd
and after you run"chroot /mnt/sysimage"