How to resolve "Unrecognised function or variable" when using LOAD function ? ( GUIDE)

load ('rawsource.mat');
a = get(handles.popupmenu4,'Value');
switch a 
    case 1
        sound (MaryHadAlittleLamb,fs);
    case 2
        sound (TwinkleTwinkleLittleStar,fs);
    otherwise
        sound (OldMacDonald,fs);
end

So I loaded a .mat file into the workplace and for some reason, variable TTLS and OMD were not regconised by MATLAB but MHALL was able to be sounded as expected. This is a callback codes for popupmenu that when user selects their choice, the selected song will play. I have also ensured that there are no typos. Also, the variable TTLS and OMD were also appearing in .mat file as expected. How can I solve this problem ?

Unrecognized function or variable 'TwinkleTwinkleLittleStar'.

Error in testing202>popupmenu4_Callback (line 449)
        sound (TwinkleTwinkleLittleStar,fs);

Error in gui_mainfcn (line 95)
        feval(varargin{:});

Error in testing202 (line 42)
    gui_mainfcn(gui_State, varargin{:});

Error in
matlab.graphics.internal.figfile.FigFile/read>@(hObject,eventdata)testing202('popupmenu4_Callback',hObject,eventdata,guidata(hObject)) 
Error while evaluating UIControl Callback.

[Walter Roberson]

For debugging, in your code immediately after the load(), add the debugging line

whos

and see which variables exist in the workspace.

Note that for this purpose the load() needs to be in the same function that uses the variables, unless you take care otherwise:

http://matlab.wikia.com/wiki/FAQ#How_can_I_share_data_between_callback_functions_in_my_GUI.28s.29.3F

[Teo Say Yee]

@Walter Roberson I did put whos after load and those variables were not in it. So I manually saved and overwrited the old .mat file. and now it is working. Problem Solved ! Thank you very much

[Rik]

In addition to Walter's remarks:

You should always load to a struct. That way it is immediately obvious where variables are coming from.