I just recently began seeing error messages in the place of a blocked ad, as depicted here in Yahoo mail ...
Quickly traced it to my Hosts File with a list of entries carrying 0.0.0.0 instead of 127.0.0.1.
All I can think of the reason for this is maybe a recent update to the Hosts file, as I simply can't think of anything else which would change the "127.0.0.1" to "0.0.0.0".
I do know that I had no 0.0.0.0 entries the last time I edited that file.
Used "Hostman's "Edit\Replace IP" menu to bulk change the long list of 0.0.0.0 entries to 127.0.0.1 ...
... and the blocked address error no longer shows.
This is all for info really in case anyone else running a Hosts file suddenly starts seeing blocked ADdress errors.
MVPS.org HOSTS file switched to using 0.0.0.0, something which Hazelnut pointed out to me when I started a topic about it. You'll just have to use your HOSTS manager software to switch them after each and every MVPS.org HOSTS File update.
Edit:
Actually I didn't start a topic about it, I posted it in the HOSTS file update topic here.