Gigapus, your tech support call ticket was originally escalated to me yesterday. Unfortunately, there is not a lot we can offer at this point. Because the Arris modem/router is leased by the ISP, and not available through any retail sources, we have no way of testing it. Also, since it is tied to the particular ISP that is local to you, we would not be able have access to the broadband network that you are on. From our limited experience with these leased combo modem/routers, the basic things to check are any firewall and quality of service (QoS) settings in the Arris modem. Turn those off if they are on.
I've been searching for any sort of documentation on the Arris modem in order to see what the settings screens look like for that product, but have not been able to find anything. It's going to be very difficult to figure out what is going on without knowing anything about that modem. In addition to the Arris product, we've had users who had similar difficulties with Actiontec combo modem/routers as well. Some users with that modem have had success setting up an ICMP port forwarding rule in the router's setup. If you are familiar enough with the Arris setup screens, you might try that.
If I recall your case, I believe your Roku Player was failing on the second step (connecting to local network). In terms of the four steps in the connection status sequence here is what is happening. Maybe this will provide some insight as to what is causing the problem:
1. Connecting to Wireless Network - This light indicates that the Roku player was able to obtain an IP Address from the DHCP server (the router).
2. Connecting to LAN - Pinging the Gateway - A single ICMP packet is sent and received between the Roku player & router/gateway. This is why turning off firewalls fixes this step.
3. Connecting to the Internet - DNS Resolution - A resolution request is sent to the DNS server for moviecontrol.netflix.com & netflix.software.rokulabs.com. This means that three name servers must respond correctly to get past this step. The name server from the ISP and then the name servers for netflix.com & rokulabs.com.
4. Connecting to Netflix - The box then opens an http connection to netflix.software.rokulabs.com for a software version check. A connection is then opened to moviecontrol.netflix.com, SSL certs are exchanged, HTTPS is established and verification codes are sent.
If all else fails, the only other option I can suggest, as someone else pointed out, is to attach an inexpensive dedicated wireless router to the Arris and let it do the wireless networking. A number of users in the same situation as you have done this and have had success. We have tested the Roku Player with a range of Linksys, D-Link, Netgear, Belkin and Apple wireless routers so there are plenty of options if you go that route.