Failure Ratio : Going into hit-only-mode?

Hi,

I'm getting the following messages in my cache.log file. There don't
appears be any problems with Squid itself (the rest of cache.log only
indicate non-critical errors).

Obviously I don't want Squid going into hit only mode suddenly like this.
I'm running Squid v1.1.22 on Digital Unix 4.0D. I couldn't find anything
in the FAQ.

Could someone tell me if this indicates a more serious problem or if there
is any way I can prevent this, thanks.

1998/07/31 18:36:46| Failure Ratio at 1.01
1998/07/31 18:36:46| Going into hit-only-mode for 5 minutes...
1998/07/31 19:03:18| Failure Ratio at 1.01
1998/07/31 19:03:18| Going into hit-only-mode for 5 minutes...
1998/07/31 19:08:18| Failure Ratio at 2.16
1998/07/31 19:08:18| Going into hit-only-mode for 5 minutes...
1998/07/31 19:13:18| Failure Ratio at 236.86
1998/07/31 19:13:18| Going into hit-only-mode for 5 minutes...

        Nick.

# Nick O'Brien, Computer Officer "It gives me a headache just to #
# Canterbury Christ Church College think down to your level", Marvin #
# Phone: +44 1227 782468 the Paranoid Android, HHGTTG #
# Email:nick@cant.ac.uk Web:http://www.cant.ac.uk/staff/nick/home.html #
Received on Mon Aug 03 1998 - 02:35:57 MDT