I recently updated my Norton Internet Security, and ever since I did, the (idle time?) notification pop-ups in the bottom right corner of the screen are interrupting my screen saver, and not allowing my computer to sleep. I turned off "Norton Task Notifications" in the settings menu, and it seems to have solved my problem. I just wanted to give you guys a heads up, just in case this issue is widespread.
I apologize if this has already been addressed on here.