Router conks out ONLY when using WDTV

(This concerns a WDTV, which is a Roku-like device from Western Digital)

I am at my wits end with this...

I have a central computer in my house running Windows 7 with a network share. It is connected to the router physically with Ethernet.

The router is a Linksys 300N running DD-WRT firmware. I've used the traffic-shaping in DD-WRT to prioritize Windows Networking and the specific IP of the WDTV.

The WDTV connects to the router wirelessly with an approved D-Link wireless N adapter.

Whenever I watch a movie through the Network Share of the aforementioned computer, on an average of twice per movie, the router's WAP will disappear completely. I haven't managed to check whether the wired portion of the router remains operational once this occurs. But the WAP doesn't come back until I physically reboot the router.

Nothing other than watching video across the LAN through the WDTV causes any kind of router trouble like this.

What the hell could be causing this?