WMI remote execution local admin

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C#

Hey all,
I have a winServer 2008 machine. I have created a new local user.
In order to make him an admin all I have to do is to add it to the "administrators" group. right?
now, I wrote a c# code that supposed to connect that local user and execute some exe file remotely.

        static void Main(string[] args)
        {
 
            string remoteMachine = "HV-BENDA";              
            string sBatFile = string.Empty;
 
            try
            {
                 string _cmd = "D:\\LocalUserManagerDLL3.5\\RunDll\\bin\\Debug\\RunDll.exe";
                if (_cmd.Trim() == string.Empty)
                {
                    Console.WriteLine("No command entered using default command for test :" + _cmd);
                }
 
                ConnectionOptions connOptions = new ConnectionOptions();
 
                connOptions.Username = "HV-BENDA\test3";
                connOptions.Password = "1234";
 
 
 
                connOptions.Impersonation = ImpersonationLevel.Impersonate;
                connOptions.EnablePrivileges = true;
                ManagementScope manScope = new ManagementScope(String.Format(@"\\{0}\ROOT\CIMV2", remoteMachine), connOptions);
                manScope.Connect();
                ObjectGetOptions objectGetOptions = new ObjectGetOptions();
                ManagementPath managementPath = new ManagementPath("Win32_Process");
                ManagementClass processClass = new ManagementClass(manScope, managementPath, objectGetOptions);
                ManagementBaseObject inParams = processClass.GetMethodParameters("Create");
                inParams["CommandLine"] = sBatFile;
                ManagementBaseObject outParams = processClass.InvokeMethod("Create", inParams, null);
                Console.WriteLine("Creation of the process returned: " + outParams["returnValue"]);
                Console.WriteLine("Process ID: " + outParams["processId"]);
 
            }
            catch (Exception ex)
            {
                Console.WriteLine("Error " + ex.Message);
            }
}

but the following exception is thrown from the manScope.Connect(); line
"The RPC server is unavailable. (Exception from HRESULT: 0x800706BA)"

when I omit
connOptions.Username = "HV-BENDA\test3";
connOptions.Password = "1234";
everything works just fine.This, as I understand, connects with my current user (which is domain admin and not just local admin). So I have tried to use these two lines with my current user credentials- but the same exception was thrown.

does anyone know how to resolve it?