I have tried: Reboot, "Reset all warnings for buying and downloading" in Account.
There are two ways to recover from this condition.
Store ▹ View My Account
from the App Store menu bar, then select View hidden purchases. Stop or resume the download.
2. Open LaunchPad and find the icon of the app you're trying to install. There will be a small progress bar below it. Click the "X" to stop the download.
Retrieving data ...