Error while evaluating UIControl Callback.

Hi i have an error when im lunching my gui. the problem happens within the uibutton group. the buttons functions are different equation that will be processed upon clicking them

function Execute_Callback(hObject, eventdata, handles)
% hObject    handle to Execute (see GCBO)
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    structure with handles and user data (see GUIDATA)
global s n v  kp kv ka e1 e2 e A B C ;
n=str2num(get(handles.Ntxt,'String'));
s=str2num(get(handles.Stxt,'String'));
v=str2num(get(handles.Vtxt,'String'));
A=str2num(get(handles.Atxt,'String'));
B=str2num(get(handles.Btxt,'String'));
C=str2num(get(handles.Ctxt,'String'));
gs=v*(s+A)/((s^n)*(s+B)*(s+C));
kp=gs;

e=1/(1+kp);
kv=s*gs;
e1=1/kv;

ka=(s^2)*(gs);
e2=1/ka;
set(handles.Kptxt,'String',kp);
set(handles.Kvtxt,'String',kv);
set(handles.Katxt,'String',ka);
set(handles.Etxt,'String',e);
set(handles.E1txt,'String',e1)
set(handles.E2txt,'String',e2);
switch (get(evendata.NewValue,'Tag'))
    case 'radiobutton1'
        num=str2num(get(handles.Numeratortxt,'String'));
        den=str2num(get(handles.Denominatortxt,'String'));
        sys=tf([num],poly([den]));
        D=feedback(sys,1,-1);
        rs = tf([1],[1 0]);
        cs=rs*D;
        impulse(rs,cs)
    case 'radiobutton2'
        num=str2num(get(handles.Numeratortxt,'String'));
        den=str2num(get(handles.Denominatortxt,'String'));
        sys=tf([num],poly([den]));
        D=feedback(sys,1,-1);
        rs = tf([1],[1 0 0]);
        cs=rs*D;
        impulse(rs,cs)
    case 'radiobutton3'
        num=str2num(get(handles.Numeratortxt,'String'));
        den=str2num(get(handles.Denominatortxt,'String'));
        sys=tf([num],poly([den]));
        D=feedback(sys,1,-1);
        rs = tf([1],[1 0 0 0]);
        cs=rs*D;
        impulse(rs,cs)
end

[DGM]

I don't see anything obvious. Without knowing what the rest of the error message says, I don't know. I can't test it either.

I also don't see why all these variables need to be global if they're also being stored in the handles struct.