How to fix GUI error?

I was working on some code and a gui for a school assignment and gotten it to work perfectly. I finished the assignment and needed to go back and change the header for basic information purposes. All I did was copy and paste a template header below the beginning function line of the gui code. Now my code is not working and get this error. This piece of code has never been a problem and idk why it is giving me an error. Didn't even edit this section, why MATLAB, why?

Error in
PS11_DragForce_calculation_yourlogin>compute_pb_Callback
(line 208)
wing_length = str2num(get(handles.wingL_et,
'String'));

Error in gui_mainfcn (line 96)
        feval(varargin{:});

Error in PS11_DragForce_calculation_yourlogin
(line 42)
    gui_mainfcn(gui_State, varargin{:});

Error in
@(hObject,eventdata)PS11_DragForce_calculation_yourlogin('compute_pb_Callback',hObject,eventdata,guidata(hObject))

Error while evaluating uicontrol Callback

edit: Let me know if you want to see what I copied to the top or how I edited the code.

[Geoff Hayes]

Ryan - did you try undoing the changes to the header? What was the template that you copied and pasted in?

[Anusha B]

Hi Ryan,

I think it would help if you share information on how you edited the code.