Proxy'ing zimbra with Apache2

[maxxer]

Hi.

Following the article on the wiki, and other resources on the net, I'm trying to have Apache2 proxy Zimbra requests.
I managed to get it work, so that all the normal zimbra functionalities are up and running.
But I still have a little issue with the social zimlet: when it tries to fetch twitter account, I get an error 500 on access.log. Digg works, but fails on twitter.
Given that I can partially ignore this error, I'm scared it could hide other issues, so I'd prefeer to make it work.

I proxed /zimbra /service /home.

In access.log I see this:

[24/Oct/2010:19:36:09 +0200] "GET /service/proxy?target= HTTP/1.1" 500 524 "http://myzimbraserver/zimbra/" "Mozilla/5.0 (X11; U; Linux x86_64; en-US) AppleWebKit/534.10 (KHTML, like Gecko) Chrome/8.0.552.11 Safari/534.10"

and nothing relevant in error.log
any idea about what could it be?
thanks