It appears to be a bug and should be fixed in version 6.4.1
Fixed Issue 2065225: NSX Guest Introspection installation fails in a NSX 6.4.0 environment with the error: "a specified parameter is not correct Property.info.key[9]"
GI deployments show installation status failed and service status as unknown for multiple hosts.
VMware NSX for vSphere 6.4.1 Release Notes