I wish I'd seen this post yesterday. I spent three hours with Comcast today and finally have my ROKU-2 working with my Xfinity Wireless Gateway (ArrisTG842). They key for me was setting the channel to 11 and changing the security setting to WPAPSKTKIP. Also, the network had to be renamed - keeping the old name with the new changes didn't work. Now my iMAC, iphone and ROKU all work and the LinkSys is no longer needed.
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