Xcode failed to download. Use the Purchases page to try again

Deleting the temporary folders as recommended didn't help. In the end I got it working again by enabling the Debug menu for the App Store app and resetting the application; it is now finally downloading the update as it should.

Steps:

1. Open Terminal.

2. Run the following command:

   defaults write com.apple.appstore ShowDebugMenu -bool true
   

3. Relaunch the App Store.

4. Choose the menu item Debug → Reset Application.

Based on steps from: https://discussions.apple.com/thread/4398074?start=0&tstart=0

It is possible that signing out (Store → Sign Out) might have solved the issue too (part of the application reset process is to sign you out) but this was not tested.

You could use the direct link to download xcode from the Developer Center: https://developer.apple.com/downloads/index.action