We've encountered a situation where items that are posted to an event's feed are troublesome to delete. First, we know that currently it's impossible to delete photos and videos through the graph API; this is not ideal but we understand this bug and can work around it.
This bug actually has to do with removing the *post* from the feed.
On a normal wall (for instance: /130157497975/feed) we see that items posted appear in the feed. If we want to remove that post from the feed, we can do that by issueing a DELETE (even through the graph explorer) of the object ID in question.
We have run into a problem through for event feeds. Here is an example: http://www.facebook.com/events/116592508456316/
(or in the graph explorer: /116592508456316/feed)
If you visit this in the graph api (or graph explorer) you can see various media posted -- images, videos, links, and text posts. We are actually unable to delete using the DELETE command for anything on this wall other than a standard text post.
Now, in our system we actually tried giving *every single* permission available that we could find to the user and we *still* get this message. Things only blow up when it's something posted on the event wall.
Again, we're not trying to delete the object (the video or photo) but just the POST about it ("such and such posted a video", etc)