I realize that this thread is old, but I'm having the same problem and found the cause:
Sonos equipment announces itself on the network using names that contain newline characters. Asus web interface builds a single string of all client names, and doesn't remove the newline characters, which in turn breaks the web interface and pretty much everything else.
I've reported the issue two months ago but have now given up on them.. anyway, just thought I'd let people know what the cause is in case someone knows someone that might get it fixed for us normal mortals eventually.
Welcome To SNBForums
SNBForums is a community for anyone who wants to learn about or discuss the latest in wireless routers, network storage and the ins and outs of building and maintaining a small network.
If you'd like to post a question, simply register and have at it!
While you're at it, please check out SmallNetBuilder for product reviews and our famous Router Charts, Ranker and plenty more!