Some web site make Varnish return a blank page

Wed Jan 27 05:07:56 CET 2010

Hi Varnish gurus:

I am new to varnish. I got Varnish working with default config with
one web site.
when I change to another web site, varnish response with a blank page.
<html> </html>
 wget can normally fetch the index.html page.

When I start varnishlog and cat varnish.log file, there are a lot of
PING and PONG. No clue what is wrong.

No other error message.

Please help me out! Thank you!

Fulan Peng