First I noticed that bash autocomplete (also known as "shell file completion") stopped working. Pressing TAB I only see the cursor to flash a little and got no filename or command expansion.
All relevant lines in .bashrc were in place and correct.
Then I noticed the TAB key was not working in any application (e.g. text editors, mail, ....): TAB was doing nothing. So it is obvious that autocomplete couldn't work as well.
So I assumed that by pressing the TAB the applications receive a wrong code. As a counter-proof I've found that directly typing the TAB code (Ctrl-I) solves the problem. Remote ssh sessions worked fine.
Started to suspect an xfce4 wrong setting...
I've found the following solution:
go to settings->settings editor;
select xfce4-keyboard-shortcuts on the left pane;
select xfwm4->custom on the right pane;
go down to the <Super>TAB entry.
You'll find it set to "Switch_window_key";
Just set "Value" to nothing (just delete the "Switch_window_key" string in it);
Hope this help!
For further info: See Xfce bug 10760