请教SQUID透明代理问题。

ww2008

各位大虾：
    我在我的LINUX FIREWALL上配置了SQUID2.6，设置好squid.conf文件后，在IE上设置代理服务器地址、代理端口后就可以使用SQUID代理上网的，但是我在iptables上设置透明代理却出现了这样的情况：
The following error was encountered:

Invalid Request
Some aspect of the HTTP Request is invalid. Possible problems:

Missing or unknown request method
Missing URL
Missing HTTP Identifier (HTTP/1.0)
Request is too large
Content-Length missing for POST or PUT requests
Illegal character in hostname; underscores are not allowed
Your cache administrator is webAdmin

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Generated Mon, 30 Oct 2006 03:24:31 GMT by firewall (squid/2.6.STABLE4)

注：（SQUID的监听端口是 17991）
iptables 规则链：
nat表
-A PREROUTING -s 192.168.10.13 -i eth1 -p tcp -m tcp --dport 80 -j REDIRECT --to-ports 17991
filter表
—A INPUT -i eth1 -p tcp -m tcp --tcp-flags SYN,RST,ACK SYN -m multiport --dports 17991 -j ACCEPT

请高手给予指点！