Disable power-saving. http://forum.tp-link.com/showthread.php?3666-how-to-solve-some-powerline-adapters-can%92t-be-waked-up-by-some-network-adapters

What kinds of VPN connection? Can you provide the current topology?

@TimW Hardware and firmware version of your W8968? Did you try to disable UPnP?

I'm afraid not. The driver has to be installed on the right PC before we connect Wi-Fi.

Download the driver first. http://www.tp-link.com/en/download/Archer-T2UH_V1.html#Driver Follow FAQ228 to install the correct driver. If you still cannot install it, provide screenshot of the error.

On your main router, channel is fixed as 1? How did you check the current channel of RE200? On Status page of its web interface, what's the channel displayed under 2.4GHz? Provide some screenshots....