this operation is not supported in the wcf test client because it uses type system.object[]
[ServiceBehavior(InstanceContextMode=InstanceContextMode.Single)]
    class Windows_processes_Service:IWindows_processes_Service
    {
        ArrayList RunningProcesses_Name = new ArrayList();
        public ArrayList GetRunningProcesses()
        {
            Process[] processlist = Process.GetProcesses();
            foreach (Process nme_processes in processlist)
            {
                RunningProcesses_Name.Add(nme_processes.ProcessName.ToString());
            }
            return RunningProcesses_Name;
        }
    }

[ServiceBehavior(InstanceContextMode=InstanceContextMode.Single)]
class Windows_processes_Service:IWindows_processes_Service
{
    public List<string> GetRunningProcesses()
    {
        return Process.GetProcesses().Select(p => p.ProcessName).ToList();
    }
}