Unlocking the Dock

Hello everyone!

I am experiencing some problems with my Macbook. The Dock was already locked when I got it and now I want to unlock it.

I tried using the app Terminal with defaults write com.apple.dock contents-immutable -bool false

killall Dock

The Dock flashes but it is still locked.

I tried also defaults write com.apple.dock contents-immutable -bool no

killall Dock

And still it didn't work.

Do you know how I can unlock it?

Thanks!