NetworkManager auto deleting client gameobject when calling it

Hi everyone, first I want to tell that my english is not perfect.

So here is my problem : I have a _GM gameobject with a NewtorkManager herited script attached, and for ClientRpc methods I use the automatically generated client gameobject.
I have already done a button in my UI that call a ClientRpc method on the client gameobject to synchronize some variables through all clients, it works.

To access the player gameobject I did a static function that return the instance of the player’s gameobject .
NetworkPlayer is the script attached to players gameobjects.
Buuut when I try to call the

NetworkPlayer.PlayerGameobject.GetComponent<NetworkPlayer>().RpcTellClientPlayerNumber(numberOfPlayer);

I get an error : Object reference not set to an instance of an object.

If I delete the line from the NetworkManager herited script, the client’s gameobject appear in my scene, if I call the gameobject, it will disappear.

There is no lines of code into the “RpcTellClientPlayerNumber(int a)” method …

Idk what to do. Is the static return of the gameobject a problem ? That just make no sense.

Thank you for reading this and eventually for a response.

PS: My NetworkManager herited script & my networkplayer script :
http://image.noelshack.com/fichiers/2016/02/1452692996-aze.png <= The LAST line of code
http://image.noelshack.com/fichiers/2016/02/1452692996-qsd.png
http://image.noelshack.com/fichiers/2016/02/1452693199-wxcv.png
http://image.noelshack.com/fichiers/2016/02/1452693145-wxc.png

I believe the problem lies with PlayerGameobject being null as it is not set before you call this line of code.
Remove the line “NetworkPlayer.PlayerGameobject.GetComponent().RpcTellClientPlayerNumber(numberOfPlayer);”

Insert this into your ServerManager script.

public static ServerManager s_Singleton;

void Awake ()
{
s_Singleton = this;
}

Then in the Start method of the NetworkPlayer Script insert

if(isServer)
{
RpcTellClientPlayerNumber(ServerManager.s_Singleton.numberOfPlayer);
}

See if that works.
Sorry for the code formating.