Can't switch workspaces

If you are using compiz, go to System/Preferences/Compizconfig Settings Manager" and lead to the "Desktop Wall" options.

Make sure you are using Desktop Wall, otherwise you may be using "Desktop Cube" in which case you should open "Rotate Cube".

In both cases, first make sure that the check box that enables the feature is activated, then properly configure your key bindings.

If they are already set and your keyboard don't activates the function, try with a different combination. Please inform if this didn't help in order to look for a different solution.

BTW: If you change key bindings and can't return to your initial screen, where "CompizConfig Settings Manager" is, try using the Super + E in order to activate "Expo", when open you can choose the desktop where you wish to go with the mouse or moving your selection with the arrow keys.

Good Luck!

A screenshot is placed here for you to see the Desktop Wall key binding config section.

Check if your Desktop Size ain't set to 1x1.

Compiz > General > "General settings" > Desktop size

Credits: Madara Uchiha's comment above, which led me to remembering this also can be an issue.

I'm posting that as an answer, because I've stumbled on it three times so far, while I've never yet had the problem with cube turned on or bindings lost.

EDIT: added an image since I have localized Ubuntu, so may be off with translations, so I'm highlighting which icons to follow. This is for Ubuntu 14.04.