Hi–I saw your post when I was looking for a solution to the same problem. It was driving me crazy, jumping around back and forth–sometiimes just when I was carrying it in my hand. But I did some more searching on the internet and found that I can press and hold the “back” button (the big one with the curvy arrow) and it will lock, and I can just do the same to unlock it. Apparently SanDisk upgraded the software to add a lock feature. (I’m thinking there was a hue and cry.) If that doesn’t work, you can download the software upgrade, and they say it will work.