Validate certificate wireless validating identity
Generate a new certificate by using New-Exchange Certificate cmdlet, or contact your certification authority to validate the certificate chain that was used for this certificate.
This status message indicates that the certificate is invalid because it was issued by an end-entity certificate and not a certification authority.
That certificate is often enrolled via an Private AD Certificate server - which means that you need the root certificate from AD to be able to trust the Radius server certificate.
AS you PC is XP Home - it isn't joined to the domain - and thus you won't automatically get the certificate.
An important motivation for using digital certificates with SSL/TLS was to add trust to online transactions by requiring website operators to undergo vetting with a certificate authority (CA) in order to get a certificate.
This status message indicates that you must enable the certificate for use in the current application.
For example, if you're trying to use this certificate for Domain Security, the certificate must be enabled for SMTP.
This status message indicates that the Microsoft Exchange Transport service was unable to validate the certificate chain, or that the public key that was used to validate the certificate signature is not the correct key.