[Sandra18[NL]]

No, it wont. You did NOT define x, y and z

Code:

public OnPlayerCommandText(playerid, cmdtext[])
{
  if(strcmp(cmdtext, "/getallplayers", true) == 0) 
  {
    for(new i=0; i<MAX_PLAYERS; i++)
    {
     if(IsPlayerConnected(i)) 
     {
       GetPlayerPos(playerid,x,y,z);
       SetPlayerPos(i,x,y,z+10);
     }
    }
    return 1;
  }
  return 0;
}

So where is the

Code:

new Float:x, Float:y, Float:z;

??