Playerprefs Question

Hey guys,

I've been trying for a few hours now to try and get a save system working. To do this i started a new test project so i could figure it out before i applied it to my actual project. I just can't get it to work. I basically want a menu with buttons for all of the levels, but make it so that you can only click on a level if you have completed the previous one. I can do all of that, but the problem is getting it to save when the game is closed and re-opened.

I would be really grateful to anyone who can help me.

If you would like to see what i have done so far, feel free to download my project.

Download project here: http://dl.dropbox.com/u/31947512/Metal%20Worm/Unity%20Test%20Project.rar