Roamio with Optimum Service

I bought a Roamio a couple of weeks ago. I had Verizon internet. It worked perfectly. I just switched to Optimum, now I can't connect wireless. It sees the router but gives me a "N02" error (can't connect to the DHCP Server). Called up Optimum they can't help, Tivo can't help either. I connected the external Tivo adapter and I could get into the router. Any suggestions I how I could get it to work without the adapter? The need the adapter for my other Tivo, and I would hate to buy another one. There not cheap.