Disable UPnP

The TD-W8901G may be getting overloaded especially if one or both clients are using p2p software like utorrent. Disabling UPnP can decrease the chance of p2p and other heavy connection overloading low-end routers like the TD-W8901G so it's worth a try.

The firmware on the TD-W8901G may have an issue that was resolved in a later firmware. Upgrade the TD-W8901G to the latest firmware available from the TP-LINK site for your hardware revision, reset the TD-W8901G's settings and configure it again.

I had same problem and I used method 1 of the following link and I fixed my problem:

http://www.tp-link.com/en/FAQ-496.html

:)