Event report on Avast free worries me!

I’ve just installed Avast a.v. free on my Windows 8.1 laptop with a view to switching to the Pro version later.
I am noticing that Windows Event Viewer reports:
Service Control Manager: The avast! a.v. service is marked as an interactive service. However the system is configured to not allow interactive services. This service may not function properly.
Would some good soul explain what it all means - especially as I’m quite new to Windows 8 and don’t know where to put my hands to find out.