If PEAP authentication is failing and the server is sending an Access-Reject message, one possible action to resolve the issue is to disable the server certificate validation on the client. This means that the client device will not check the authenticity of the RADIUS server's certificate, which can sometimes resolve connection issues, especially if there is a problem with the certificate chain or trust settings. However, this should be done with caution as it reduces the security of the authentication process. References: CCNP Enterprise Wireless Design ENWLSD 300-425 and Implementation ENWLSI 300-430 Official Cert Guide