[squid-users] Is (CACHE_FILL_OPEN_FILE) a squid eror message?

Hello,

Recently I've been getting the following :

 Server Error
 The following error occurred:

 An internal error prevented the object from being sent to the client
 and cached. Try again later. (CACHE_FILL_OPEN_FILE)

 Please contact the administrator.

Is this a squid error and what's causing it if it is?
Any idea what it is if it's not squid?

Thanks.

-- 
John Francis Lee <jfl@robinlea.com>