Here´s my Post from last Year that helped me. Important is the right stripped Firmware with the right name and size 
Quote:
It´s very easy to recover the Archer C7 by TP-Link TFTP recovery mode. Please go ahead with this Documentation -> TP-Link TFTP recovery mode and firmware (TP-Link Archer C7 V2)
Total time for Recovery: max. 10 Minutes
RecoveryFile Name for INT/EU/DE Version -> ArcherC7v2_tp_recovery.bin 16.252.928 14.04.2015 20:34 -a--
Source was from -> http://www.friedzombie.com/tplink-stripped-firmware/
Alternate Firmware-Link with tftpd32: HitMe