Previously master w8980n didn't need any wds settings to work perfectly with TL-WA850RE range extender. WA850RE it is typical repeater however. W8960N like W8980 are typical ADSL routers and radio...

Your main router is? Can you give us screen shot from your settings? W8980 and W8960N have different chipset and I think that is main problem in WDS configuration.

I think that is problem with "https" - (web secure protocol). I don't know a solution for it in original firmware.

Do you have latest firmware on the router? Can you enter some DNS addresses in DHCP Settings tab?

Have you made reset to factory settings?

Please - http://www.tp-link.us/article/?faqid=603 and http://www.tp-link.com/app/usb/download/How to Use the Media Server.pdf