This is the site I admin, and I pasted a code into Advanced CSS to hide the Latest Activity feed from members profiles. Look to the bottom of the screen shot and you'll see the code shows up at the bottom of the page. I know others are using this same code, so I'm asking i anyone else is having this problem.
Update: Turns out there are two hacks down there, not just one.
The code is right but it looks like you have put it in the Custom Code
Every hack I have ever used to hide Ning modules have all been placed in Advanced CSS, this is the first time I've had this problem with any of them. I'll see if it works.
Good thing, we have Jen:)