Weird 404 error during set up

I had this same problem. The reason I was getting kicked out of setup was my cable modem/router was reassigning my Netgear extender a new IP address during setup. Since I was accessing my extender through its default IP address ,(In my case, 192.168.1.250) once my cable router gave my extender a new IP address, I was given the 404 error or a timed out error. [Fiddler] The socket connection to 192.168.1.250 failed.
ErrorCode: 10060.
A connection attempt failed because the connected party did not properly respond after a period of time, or established connection failed because connected host has failed to respond 192.168.1.250:80  

The solution is to locate your extender's new IP address that your cable router gives to it. I went into my cable router, using my browser, and saw what addresses it was giving to my connected devices and simply guessed as to what the new address would be. My (Comcast) cable router IP address is 10.0.0.1. It gave my extender the IP address of 10.0.0.2. Once I guessed this and entered that address into my browser, I connected to my now setup router and all was well.