I’m having the same problem. And, though it seems pointless to post it here due to the responses I’m reading, here is the issue:
I’ve been watching anime all week long just fine on several sites. Suddenly I get the error media file not found message. It was rare at first but now its nearly every other episode. I KNOW the episodes are there because I’ve watched them all before not to long ago. I also tried it on my phone and it worked fine. Its not my security because the problem is new and there have been no updates. Also, the message prompts when I skip ahead in videos to certain points. So what’s going on?