Login problem in Linux : GDM could not write your authorization file

Some times when you login into your linux system, through XWindows-(GUI Mode) you will get
the following error message:

" GDM could not write your authorization file . This
could mean that you are out of disk space or that your
home directory could not be opened for writing . In any
case it is not possible to login. Contact system administrator ."

This will not allow you to login into your system,but you can login as root user.

The reasons for this error and solutions is as follows:

First Reason:
The space allocated to / partition may be filled with data and there may be no space for storing files.Use df -h to see the disk usage.If the disk usage of / partition is near to 100% (may be 90% to 100% -depends upon the space allocated),then this login error will occur.

Solution: Free the disk space by taking back-up some unwanted files, keep down the disk usage to 50% to 70% and then reboot the system

Second Reason:
The /tmp file may not have rwx permission for user,groups or others.While user logins into The XWindows(GNOME or KED),it will write some files like gconfd-(username), xses-(username).3JSxMF , so the user who logins into system must have write permission to /tmp directory ,othewise the system will not login

Solution: Login as root and give rwx permission to all users, for this give the following command : chmod 777 /tmp and reboot the system

Third Reson :
A file in your(user's) home directory called .Xauthority may not have proper permission

Solution: Go the users home directory and give the command :
chmod u+rw .Xauthority and the reboot.