Error 500 on index.php?module=Proxy&action=getJs

Hi,

I'm new with piwik.
I'm using :
- Linux raspberrypi 3.6.11+ #474 PREEMPT Thu Jun 13 17:14:42 BST 2013 armv6l
- Apache 2.0
- 5.4.4-14
- Piwik 1.12

On some pages, no buttons and no component works.
On Chrome, I see in the console the following error:

GET http://homepi.fr/piwik/index.php?module=Proxy&action=getJs&cb=1ef8037cd582dafeb9f3ee2b2dd01fb6 500 (Internal Server Error) index.php:21
Uncaught ReferenceError: SitesManager is not defined index.php:218
Uncaught ReferenceError: $ is not defined

This seems to be a problem loading javascript.
Do you have an idea to help me please?

Thank you