Squid - Serving stale pages
 

I am having problems with my squid server serving out stale pages every so often, I have around 1million requests per day on the server and from what I can tell it only happens probably once every 15 days or so I will get a call where someone is getting old content. If I go to the page it will be old content, I can go to it with netscape and do a refresh and it will refresh the cache server. What could be causing this? It does not happen very often but enough to be annoying, my server is running as a transperant server.

I am running redhat 9.0 with squid-2.5.STABLE4, I don't get any errors in any of the logs, just every so often I get a stale page, is there any way around this?