XP is no longer supported by Microsoft (no more security patches) and is seen by most organizations as a security risk. As an organization, we have a no XP policy.
Its possible that with the update to PCS that eliminates significant vulnerabilities, the patch was never applied to XP so it is not going to be allowed to connect thus protecting the enterprise from this vulnerability.
You should be able to roll back to the previous PCS version in the appliance administrator login (System Maintenance > Install Service Package > Upgrade/Downgrade). Though this not recommended as it will open the enterpriose to significant risk.
What is the version of the host checker component?
New version of the host checker component will not work with Windows XP.