This absolutely worked for me, after hours and hours of failed attempts. Thank you!This seems to be due to an interrupted or corrupted download. This can usually be resolved by clearing your Mac App Store cache.
this worked for me. downloading again now
- Quit the Mac App Store
- Go to Terminal and type following: open $TMPDIR../C/com.apple.appstore/
- Move the files inside the folder to the Desktop or any temporary location (if you are confident, you can move them to Trash straight away.)