Thank you, Matt G.
My 211 has always been plugged directly into the electrical outlet. There are no ethernet cables connected to it. Before I installed my (TP-Link) powerline adapter, the Homeplug was plugged into the wall (in a different room from the 211) and connected to my router via ethernet. The 211 indicated that it had an internet connection.
When I replaced the Homeplug with the TP-Link, I checked the 211 and it was not connected. I think I followed procedures to try to connect it, but was unable to do so. If this is supposed to work, then I'll try to reconnect it again. There's always a chance I messed something up the last time I did this. Should I unplug the 211 and plug it back in to reset it before I mess around resetting the connection?
And, by the way, unless I'm misunderstanding you, there has to be a way to get ethernet into the powerlines in my house or the 211's onboard system won't work, right? That would require that some device be plugged into a wall outlet somewhere, and that my router be connected to it via ethernet. In my case, that device was formerly a Homeplug unit installed by the dish Tech, but is currently a TP-Link powerline adapter.
Thanks again for your help.