Xcode 4.1 can't reinstall. App store says “installed”

Question

Today i update my system to Lion and try to update Xcode. After downloading from app store i get error.

So i remove my old Xcode 4.0 by this command

Answer 1

When I downloaded Xcode from the Mac App Store it created an Icon in launchpad called 'Install Xcode' and you're able to kick off the install from there.

My installation failed the first time and I was able to reinstall fine.