Did you upgrade the correct firmware? No power cut-off during upgrade? Reset won't help? http://www.tp-link.in/support/rma/

It is not available anymore on their website. You may try to get the old firmware from TP-LINK support team. http://ticket.tp-link.com/index.php?/Tickets/Submit

Try to change some settings on web interface of TL-WR1043ND. Not sure if it helps. Channel---1, 6 or 11 Channel Width---20MHz

I'm interested...How did you make it? I read your thread before but I have no idea and I thought it should not be router's job...:)

Is it possible for you to test wired connection to WDR3600? How many wireless clients are connected? Are they all connecting to 2.4GHz, or dual bands? Try to change the channel to 1, 6 or 11, channel...

Impossible. Password should be the same as the main router but the SSID can be different.