Why is Avast now blocking Facebook on my pc?

Attempting to go to Facebook (many times over several hours) but experiencing long (indefinite?) waits with NO notification from Avast (same on IE & Chrome). Switched Avast off & tried again & was able to gain access to Facebook. There have been no changes recently (apart from standard Windows 7 Home Prem updates).
Anyone help please?
Thanks
Frank

UPDATE:*** problem went away on IE and (eventually) on Chrome ???***** not sure why - apologies for any inconvenience