[squid-users] what does this warning means?

Hi list,

I always have this messages on my cache.log, but i've never been
worried about them, it is just curiosity to know what this means and
if I can solve it:

The message is:

2011/02/25 09:53:53| WARNING: HTTP header contains NULL characters
{Accept: */*^M
Content-Type: application/x-www-form-urlencoded}

Thanks a lot
Received on Fri Feb 25 2011 - 09:39:26 MST