You can use this utility to help you log into the management webpage of WPA4220:
http://www.tp-link.com/en/support/download/?model=TL-WPA4220&version=V1#tbl_b

Hi, I managed to fix the issue yesterday.

For anyone else having a similar issue you need to set yourself a static IP. To do this go to the Network and Sharing Centre > Manage Wireless Adaptors > right click the wireless adaptor and choose properties > edit the IPv4 service > Enter 192.168.1.100 into the IP address and 255.255.255.0 into the subnet mask > Press Apply & then OK. Leave the DNS fields as they are.

Go to the browser of your choice and navigate to 192.168.1.1 and you'll be able to login to the extender.

*You will not have internet access whilst doing this. So once the changes have been mad you need to repeat the above steps, but remove the static IP and subnet mask (just click the option to automatically obtain an IP)