I have tried to upgrade my firmware version and whenever I upload the updated firmware file it shows a error code 4503 and an error message " The file is not accepted". 

I want to upgrade my firmware version because this router isn't working as range extender mode. When I connect this router to my main router wirelessly internet connectivity of both the router came down and sometimes the devices that connected to this router and my main router gets disconnected and keeps on showing connecting but never connects.

And once I switch off this router Archer C20 my main router starts working absolutely fine. And this problem happening with every router as I have tried to use it as range extender in my friend router too. 

Please resolve this issue asap!

It's been a just 9 days since I purchased this router and this problem is happening from day 1st. 

Really fed up with this tp link router!