Thank you for your message.
It might be that the Host service (and/or other Host files) was somehow blocked (or even deleted) by the antivirus software. Please try fully uninstalling
Host as described here
and re-installing it from scratch. After re-installation, please make sure to add the entire Host installation folder to the exceptions list as described here
In addition, perhaps this troubleshooting guide
from our KB might provide some helpful information as well.
Let us know if the issue persists.