We have Frontier FiOS with an Arris NVG468MQ router.  We recently dropped FiOS TV (and Frontier is dropping it everywhere), kept Frontier FiOS internet but added basic Spectrum (copper).  We have an Arris AM525 to extend Wifi to the opposite end of the house but when the Spectrum folks hooked up the TV they just disconnected it.  We have crappy Wifi at that end of the house again so I plugged the co-ax back in and it seemed to fire up good.  When I did a Wifi analyzer the signal strength was off the charts.  But now we cannot log into the Wifi from there.  We can see the Wifi network, the signal strength is super strong, but it absolutely will not accept the WAP key.  WAP key works with other extenders but absolutely not with that.  Tried with several devices and with my cell phone, will not connect.  Not sure why we can see the Wifi network but cannot log into it now.  There is a WAP key on the AM525 but it will not accept that either.  

Not a networking expert but not sure if there is some setting I need to do in the router or something I need to do on the Am525.  Any and all help would be GREATLY APPRECIATED!

Thanks in advance for your help.