So immediately after set-up I signed up for Netflix via my computer and went thru the RokuHD Netflix sign-on
Entered my Netflix email address and password but it didn't go thru. Retried it and still no go. Then started a chat with RokuHD online help and got it resolved! Simply uninstall Netflix from RokuHD, plug out the RokuHD box and wait for 5-10 seconds. Reconnect then reinstall Netflix. Now open up Netflix and log in again with your Netflix email and password. Bam! It worked with no problem at all.
Hope this helps as I couldn't find an answer online myself. One tip... you don't need to put any activation codes or anything on the Netflix.com website via your computer.