Error with GUI window

I have a GUI window with only two push buttons. Upon clicking the first, the callback will generate a uidir to select a folder from which to work. Then the file will be reformatted and saved as a collection of smaller files. This works well. The other pushbutton is simply intended to close this current window and open another. The problem is that when I open the figure and press pushbutton one i get the following error:

Undefined function 'Window_one' for input arguments of type 'char'.

Error in @(hObject,eventdata)Window_one('pushbutton1_Callback',hObject,eventdata,guidata(hObject))

Error while evaluating uicontrol Callback

From my previous experience making GUI windows, this likely means there is a shortage of handles and I have put nothing in the opening function of the code. However, I have not used the handles structure to refer to any of the variables in the code as they do not need to be shared among other callbacks and do not affect a figure. Do I need to add handles structure to some of the variables (though I don't see where i would) and add them to the opening function or could the error be due to something else?