Hey guys. I'm having a similar issue:
My PS3 suddenly locks up now when I attempt to stream video from my DNS-323, but ONLY when I attempt to start a video from browsing the folders. This DOES NOT happen if I tell the PS3 to show me "All Videos," and begin streaming from that option, even if that video file freezes the PS3 from the browsing folders option. My Xbox 360 can still stream videos from either option.
I am using the DNS-323 with 2 1TB Seagate Serial ATA hard drives, and running firmware 1.08. I also am using a 250GB PS3 Slim with firmware 3.15. They're on a network run by the DIR-825 (firmware 1.13NA), and all hardwired. I've heard that the PS3 can only play video files from a USB if they are in the root folder. Maybe this is similar?