mod rewrite - Apache mod_rewrite doesn't work

I have to proxying all request via mod_rewrite from an apache to another.

loaded mod_proxy and mod_rewrite and I configured apache as follow :

    Options  +FollowSymLinks -Multiviews
    ......
    RewriteEngine on
    RewriteRule ^/abc/(.*)    http://anotherhost/abc/$1    [P,L]
    ....

but the apache return me 505.

this is what Apache writes on rewrite log:

- - [16/Sep/2010:14:13:06 +0200] [myhost/sid#7f9472e763b8][rid#7f94731a6c78/initial] (2) forcing proxy-throughput with http://otherhost/abc/
- - [16/Sep/2010:14:13:06 +0200] [myhost/sid#7f9472e763b8][rid#7f94731a6c78/initial] (1) go-ahead with proxy request proxy:http://otherhost/abc/ [OK]

and this on error log:

[warn] proxy: No protocol handler was valid for the URL /abc/. If you are using a DSO version of mod_proxy, make sure the proxy submodules are included in the configuration using LoadModule.

What I'm missing?

Answer

Make sure you've loaded both mod_proxy and the supporting modules (i.e., mod_proxy_http).

Best of luck!