Since you dont mention what version your using of the appliance, I will provide the answer for the 2000 model.
36 CacheFlow Inc.
Client HTML Requests Fail
When a request for a Web document fails, it indicates one of the
following:
? the Web browser is not properly configured for the
CacheFlow 2000
? the CacheFlow 2000 cannot access the requested document
? the CacheFlow 2000 is not properly configured
? the CacheFlow 2000 is not functioning
To try and locate the problem, follow thesteps outlined below:
1. If the CacheFlow 2000 is used to access the Internet, and the
CacheFlow 2000 has been working properly, the most likely
cause of failed requests may be the route between the
CacheFlow 2000 and the Internet or intranet. Before you spend
time troubleshooting the CacheFlow 2000, verify your
connection to the Internet using the ping and traceroute
commands from the command line interface. If you are able to
ping the destination from the CacheFlow 2000, use the testcommand to verify the device can get the object. For
information on the ping, traceroute, and test commands, see the
CacheOS Management and Configuration Guide. If the request
fails, try other HTML requests to verify all requests fail.
2. The CacheFlow 2000 can be configured to deny access to
address groups. If the CacheFlow 2000 is configured for
forwarding or filtering, verify the requested address does not
match a denied subnet and mask. To configure deny settings in
the Web interface, from the home page select Management, then
ICP/Forwarding.