Maybe the table is full, the entry is dulplicate or operation is incorrect etc.. No worries. The switch is still running properly.

All powerline device have been paired? How about status of powerline light on all of them? http://www.tp-link.com/en/faq-258.html If they are paired but no internet connection, try to configure...

If you turn off RE200 and connect to the main router directly, the OpenVPN client can connect? Are you using static IP or dynamic IP on web interface of RE200?

Hard reset it first. Reconfigure it step by step. In some case, if backup file is used, it may cause the problem like yours.

What's the hardware version and firmware version of your WR841N? Firmware is up to date or not? Connect the modem directly to your PC and try to set up a PPPoE connectoin on your PC. If it works,...

Either WPA2220 or WPA4220 can work with PA211. No worries.