Switching tty shortcut

I recently installed Ubuntu Natty (11.04) and now pressing Alt+Left/Right arrow key switches my tty to the adjacent one. How can I reconfigure the keyboard shortcuts so that this stops happening?

Update: I enabled Ctrl-Alt-Backspace restarting X. Now when I start my computer and then restart X, this problem stops occurring. However, if I don't restart X after starting my computer, this problem persists.

Another update: reinstalling the system fixed the problem.

Solution 1:

Click on the application icon on the Unity bar. Type keyboard and double click on the entry labelled as, "Keyboard Shortcuts. Scroll down the list until you get to the item that says, "Move window one workspace to the left". Click on each of items and change the shortcut to your liking.