Reports of this bug are usually accompanied with the output of brew cask list showing the cask is indeed installed. You should not rely on brew cask list anyway, and this error is somewhat related to it.
This is prone to happen when you try to uninstall a cask that has been updated since you last installed, or when a cask no longer exists in the repo (brew cask list will show it with (!)). We鈥檙e working to handle those situations better.
For now, rerun your command with --force, or uninstall manually.
Do not open an issue.