Getting this the last few days:
Changing browsers didn't fix it (Chrome + Firefox), changing computers didn't fix it, clearing browser cache+flash cache didn't fix it, etc..
Happens when starting a new adv ... the adventure picture doesn't load for the little pop-up window. Then, on the adventure, when something changes (for example, giants battle, repair the bridge, get the error and the bridge doesn't show up - same with killing a leader where it would load a new image). Isn't just limited to Giants Battle, happened also with Twins I ran as a test.
Just started happening fairly recently, so I am guessing something changed on the server end?
Others in guild reporting the same problem (but not everyone - yet).