The fixperms script will fix the symptoms but may not fix the core issue.
If this happens often, someone or something has likely damaged your Centova Cast installation and you'd want to consult the Disaster Recovery article in our KB.
Either that, or someone is putting files in the spool directory from outside of Centova Cast, and is not observing proper permissions and ownerships. In which case, someone should be sternly reprimanded.
Either way, this won't spontaneously occur without external interference by another app or system user.