Please make sure you run the game, and the bot, as Admin. If you have any anti-virus running, you'll most likely need to add an exception for Hearthbuddy. We do some things that some viruses also do, so there can be some false positives at runtime.
Technical answer: The bot is trying to attach to the game, but it's unable to set up some things because it is being blocked by the OS, or some external program. (Typical access rules block this)
Edit; Run the Blizzard launcher as admin, to make the game launch as admin. Forgot to note that, sorry!