What does a solid orange light mean on your router? Did you pair the two powerline units? Are the two powerline lights on? You can refer to the videos on the website：...

The router doesn't support Net-Bios（Hostname）, but as LLMNR protocol, you can ping hostname on windows devices, but cannot do it on Mac OS or Linux.

With WDS, you should be able to connect to the Linksys wifi. Why did you say you can no longer get Wifi access through the Linksys router? Is the wifi name on the TL-WR841N the same as the Linksys?

You can check the spec on the website: http://www.tp-link.com/en/products/details/cat-5258_HS110.html#specifications

try the firmware recovery like this post show, http://forum.tp-link.com/showthread.php?81462-How-to-recovery-the-router-when-you-bricked-it&highlight=fitz if no luck, contact tp-link email support.

what is the current firmware version of both not-working plugs? can you show us a screenshot of that invalid argument? do they all connect to the same Wi-FI?