Error 4 is almost always displayed when the connection between AiPort Utility on the PC and AirPort Extreme is blocked.
The usual culprit is the Windows Firewall, but the anti-virus software, and Microsoft Security Essentials....if you have it installed.....can do the same thing.
Start with the firewall and check the settings to see if you can set up or allow an "exception" to allow AirPort Utility to connect to the Extreme.
Windows Firewall from start to finish - Microsoft Windows Help
Check settings on the anti-virus and MSE as well.
Worst case, you may need to turn off the Firewall, anti-virus, and MSE to configure the Extreme, then turn them back on once the Extreme has been set up.
I don't have Windows 8, so things may not be exactly the same as I described. Maybe a Windows 8 user will post with a few more tips.
One thing that may help is to connect an Ethernet cable from your PC to one of the LAN <-> ports on the AirPort and try things that way.