Hi,
ok, import that package attached to this post. It's a fully working sample with three level buttons,
use the level manager and its inspector interface to unlock levels, lock them alls. Click on the unlocked levels to callback the level manager with the name of the level to load, locked level will not callback the level manager,
so, pay attention as to how the prefab is made of for the level buttons, and how it all communicates. Note also that I do not make use of global variables, just to show that it's possible to get away with having to use too many global variables when it's not necessarly needed.
if you have questions, don't hesitate. If everything is clear, I'll put it on the user wiki, I think it's a good sample.
EDIT: now with player prefs to save level.
bye,
Jean,