Mongodb 500 Internal error

Hello Allan,
I'm decided to use a database where my data is stored now :)
I use this php script http://datatables.net/development/server-side/php_mongodb in order to get the rows.
On localhost with mongodb on localhost too .. it works.
but when I use a distant mongodb like : $m = new Mongo('mongodb://mongo-1:27017');
(no user ... no password ... it's normal)
I get a 500 internal server error from my apache ... the connection looks good ..
But with phpMoAdmin (on the same apache server) I can see the datas ...

Please you can help me ?