It is because there is a bug on Ubuntu 10.04.1 (the latest version of Ubuntu) and it can be fixed easily.
You can check the version of Ubuntu by issue the following command.
Step 1 :
Login and open a terminal. Issue the following command.
You will note that the ownership of the following directories have changed to root:root instead of username:username, e.g. samiux:samiux.
Step 2 :
Fix the problem by issue the following commands.
sudo chown samiux:samiux .bash_history
sudo chown samiux:samiux .config
sudo chown samiux:samiux .dbus
*Replace "samiux:samiux" with your username.
Step 3 :
Log out and re-login. The problem solved.
That's all! See you.