I had this problem before adding the NVR's IP address to the site list in the Java Security Settings:
http://forums.dlink.com/index.php?topic=57476.0
I'm not certain, but I think another issue might have been the way I originally configured my new router. (I also purchased a second router to handle the camera traffic.) Originally, I had it set up as a router (incoming network plugged into WAN port, had its own subnet), when it seems to function better as a switch\wireless access point (incoming network plugged into LAN port and DHCP turned off, so the "parent" router handles the DHCP and everything's on the same subnet).