Just installed on Archer C7 V2(US). Had a lot of problems installing DD-WRT and thought I would show what worked for me.

I had been running it with the TPLINK stock firmware for a couple years and had updated to the latest factory firmware. When trying to install the factory-to-ddwrt.bin file I kept getting the 18005 error. Looking it up it seems this is because the later factory firmware tries to lock out unapproved updates. I tried to downgrade to several older versions of factory firmware and got the same 18005 error.

I read through this thread https://forum.dd-wrt.com/phpBB2/viewtopic.php?t=287073 and several posts detailed very complicated procedures that seemed more trouble than I wanted to try. One post by "eginnc" sounded simple so I tried it.

He started with factory firmware 160719 so I went to TPLINK, downloaded that version, and it installed ok on my router. I then went to http://download1.dd-wrt.com/dd-wrtv2/downloads/betas/2017/04-24-2017-r31899/tplink_archer-c7-v2/ and downloaded factory-to-ddwrt-US.bin since that was the file he used. I powered on the router with the WPS/reset switch pressed and held it for 30 sec. Then was able to connect to factory configuration pages and do a firmware update using the r31899 factory-to-ddwrt_us.bin and it worked. I then was able to update to DD-WRT build 41892 from the DD-WRT config pages and it is working fine for me.