, you can refer to http://www.tp-link.com/resources/document/TL-PS110U_Compatibility_List_2.pdf If you have installed the printer server correctly, you will see the printing language like this picture

Most rings will not block the powerline data. My suggestion is to put the fourth PA251 to the same place together with other three PA251 to assure that the fourth one has successfully joined the...

that is weird. How do you connect the powerline adapters to the other devices? for example, A connected to the router, B connected to the PC..

Try to change the channel and see if it works

Can you find the following option on the MFP and Storage Server software?

Have you tried to download a new software from the website? also uninstall the antivirus first.