Set up a TFTP server on your computer and upload the TP-Link stock firmware to the router.
Even though your router is not “bricked”, this tutorial works for reverts as well…
http://forum.tp-link.com/showthread.php?81462-How-to-recovery-the-router-when-you-bricked-it1
Rename the stock firmware file wr841Nv13_tp_recovery.bin