You're not the only one. We've had exactly this issue show up at two customers yesterday, both also using Windows 7 client and we have not made any changes at all. In one case, the wireless profile is pushed with a GPO. In the other case, it's a guest network that's not pre-configured. We fixed the GPO by selecting the appropriate Root CA under PEAP settings. The strange thing is there were previously no Root CA's selected and the GPO had not been changed since september. We're still looking into what has changed last weekend that triggered the error to start popping up. Possibilities we're looking into are windows updates for Windows 7, windows updates for the Windows NPS server (also DC) and possibly a certificate used (signed by AddTrust). One other coincidence is the NPS/DC auto-enrolled for a new certificate last weekend.
