When a proxy cache configuration is tied to a PVS server, and you reinstall XenServer on the host that had the proxy cache configuration, PVS and XenServer become out of sync. This occurs because the reinstallation of XenServer wipes the previously configured proxy cache configuration.
In this scenario, PVS assumes that the proxy cache configuration still exists, and when the Streamed VM Setup Wizard is used, it fails, indicating that the provided UUID (associated with the proxy configuration) is invalid. For this reason, the user must delete all previously configured VMs associated with this cache configuration, including the host. After accomplishing this, reconfigure PVS and setup the cache again.