Problem with open serial port

Hi,

I am doing a project and i need to recieve data from microcontroller.

I opened a new GUI file in Matlab, but when i get to open the serial port i get this error:

"Error while evaluating UIControl Callback"

Somone have an idea what can be the problem?

Thanks.

This is my code: The problem is in case 3:

function pushbutton1_Callback(hObject, eventdata, handles)
% hObject    handle to pushbutton1 (see GCBO)
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    structure with handles and user data (see GUIDATA)
axes(handles.axes1);
cla;
s = serial('COM4','baudrate',9600,'Terminator','CR','StopBits',1);
popup_sel_index = get(handles.popupmenu1, 'Value');
switch popup_sel_index
    case 1
        plot(rand(5));
    case 2
        plot(sin(1:0.01:25.99));
    case 3
         fclose(s);
        delete(s);
        clear s;
        fopen(s);
        fprintf(s,'Telemeter@');
        distance = str2double(fscanf(s,'%s'));
       %a = '5';
       str = get(handles.text1,'String');
       set(handles.text1,'String',[str distance]);
       fclose(s);
end

[Walter Roberson]

After you clear s then it no longer exists as a variable so you cannot fopen it.