setting up a basic mod_proxy virtual host
Solution 1:
Looks like you're not loading the mod_proxy_http module (which is needed to proxy to HTTP servers). I don't have Ubuntu 10.04 in front of me, but IIRC it's something like:
sudo a2enmod proxy_http
Solution 2:
The above answer didn't help for me as I was receiving the same error as in the author's comment in the selected answer. However, I did find the following post and change which solved my problem:
sudo /usr/sbin/setsebool -P httpd_can_network_connect 1
Source: http://allscm.com/archives/apache2-proxy-disabled-connection-on-localhost.html