I have just installed a similar printer for a friend and came across exactly the same sort of problem. In the end I went into the router and changed the password then used the new password when asked for using the install wifi printer wizard You will need to access the log-in admin pages of your router - the IP address could possibly be 192.168.1.1 or 192.168.0.1. or something similar. You should type this into the address bar at the top of the browser (not into the Google box) and this should lead you to a log-in screen. If you have not changed the password then the default is usually: password and username: admin.
Best Cyber Monday deals 2015 live blog: Best UK Cyber Monday tech deals, sales, discounts & offers