Linksys Wireless Router :: EA4500 Guest Network Re-authentication Doesn't Work

I have successfully set up a guest network on my EA4500. Guest laptop associates with guest SSID just fine. Then via IE, it gets prompted for the guest password, which is entered and accepted just fine. At this point guest laptop is on the network.
 
BUT... at some point the guest laptop will need to reauthenticate (I don't know what the timeout is, but maybe one or two days?). Anyway, it's at this point that IE presents the guest network login page. But now after typing in the password, "enter" or clicking on the button does nothing. It looks like the guest web page doesn't get loaded properly or completely, so the reauthentication can't complete, therefore can't get to the internet. So, while in this state, I've also tried Firefox and Chrome, and same thing, no action when trying to submit the guest password. Tried rebooting guest laptop, and still same problem. Only thing I've found so far that works is to reboot the router. So I'm guessing there's a problem with the guest/web server on the router?? It's a real pain to have to reboot the router every day or two, when I've had other Linksys routers run for months without having to touch them.
 
I was running CCC 2.1.38 when I first noticed the problem. Since then I've downgraded to Classic 2.0.37, but it seems I still have the same problem. Again, I can connect & authenticate just fine initially, but when reprompted after some period of time, it doesn't work.
 
I've tried contacting Cisco support, but it looks like I'm at 91 days since purchase and thus outside of my 90-day complimentary support, so they happily provided me with the premium support options just to have the honor of talking with them. Guess I shouldn't have spent so much time trying to figure this out myself.