Non player objects movements are not syncronized on server

Hi everyone I'am struggling with this problem from a very long time.

I have a scene object (a cube) that can be moved by the client. The problem is that its movements are not seen on server.

The cube has a network identity and network transform component. To sync its movements i'am using [command] (based on the example I found here http://docs.unity3d.com/ScriptReference/Networking.CommandAttribute.html).

I've found out that the problem is that, the statement:

if (NetworkServer.active)

is never true.

Could anyone help me please? Thank you so much