What happens:

When I log in into my Ubuntu everything is normal, I have some icons on my desktop and I can see them at this point of time. As soon as I click on the explorer (nautilus) on the Launcher bar, everything goes (disappers) and never comes. No matter how many time you click on the launcher, you can't open nautilus.

I tried opening nautilus from the terminal, get the following:

santosh@santosh:~$ nautilus
Initializing nautilus-gdu extension
** (nautilus:2158): DEBUG: SyncDaemon already running, initializing SyncdaemonDaemon object
Initializing nautilus-open-terminal extension

(nautilus:2158): Gtk-CRITICAL **: gtk_action_set_visible: assertion `GTK_IS_ACTION (action)' failed

(nautilus:2158): Gtk-CRITICAL **: gtk_action_set_visible: assertion `GTK_IS_ACTION (action)' failed
Segmentation fault

I suspect on "Segmentation fault" on the last line, whats that?

I was amazed when I run this command in sudo.:

santosh@santosh:~$ sudo nautilus
Initializing nautilus-gdu extension
** (nautilus:2216): DEBUG: Syncdaemon not running, waiting for it to start in NameOwnerChanged
Initializing nautilus-open-terminal extension

(nautilus:2216): Gtk-CRITICAL **: gtk_action_set_visible: assertion `GTK_IS_ACTION (action)' failed

(nautilus:2216): Gtk-CRITICAL **: gtk_action_set_visible: assertion `GTK_IS_ACTION (action)' failed
Nautilus-Share-Message: Called "net usershare info" but it failed: 'net usershare' returned error 255: net usershare: cannot open usershare directory /var/lib/samba/usershares. Error No such file or directory
Please ask your system administrator to enable user sharing.

As soon as I type sudo nautilus and hit enter, nautilus starts and the desktop background changes (to the default which ubuntu has). Don't know why but at this point as soon as I click on Desktop (from the left pane) then nautilus closes.

Did anyone has same issue? I am corrently working with commandline to do my work and its a big pain.

Additional Information:

Another thing I have noticed that when I want to open the location of PDF file I am reading in document viewer (by clicking the folder icon). It gives error "Could not open the containing folder" and "Failed to execute child process "nautilus" (Permission denied)". Any idea?