Log admin
Pass admin
Thats for Tp-Link products as default
Read step #2 here http://www.tp-link.com/en/article/?id=87

Thank you for your advice. But i do not think that is not the solution i need. I called the support and got a solution from them just now and fixed the problem.. The support girl guided me log into the page and changed my security setting from Automatic to the specified on for my router. My router is using WPA2-Personal, AES. She changed it on my range extender security setting to the exact same as the wireless router.

cora u posted on #1 configured it properly. It works for my Window 7
then u posted on #3 She changed it on my range extender security setting to the exact same as the wireless router.
so for what I read, you never configured properly, as you posted.on #1

Hi guys, im having the same problem..
When i try to connect to my WLAN through the AP it asks for username and password.
I have gone over the security settings of my router and they match the settings of the AP but still no luck...
And i have tried putting in admin admin for username and passwd but it doesnt work.
What can be done to fix this problem?