I also have this problem (cant view from local network). From outside my own network, using port 80 i get as far as the blue log in page but when i enter the password and press log in it seems to start the connection process but then get "connection failed" error message, the dvr is connected to the Comcast cable/modem by ethernet cable, so connection IS solid.
With the help of Comcast "Signature Service" tech support>>>I tried one of the suggestions and played with re-assigning to port 88 and then also tried port 8080, no luck there (I dont even get to the blue log in page). On the second try, i even had the Comcast tech actually set up ports for me (remote access) and he "thinks" there might be something defective with the cable/modem preventing/not allowing the ports to open, he recommended to have the unit exchanged. He said he has assisted a handful of customers with their monitoring set ups but never assisted a customer with the type of modem we have, the newer SMC cable modem with built-in wifi.