Pankaj - yes, I see that button. I also see, in your m file, lots of pushbutton callback function that have no bodies which seems to suggest that your GUI has had a number of pushbuttons that were added and deleted. In this case, pushbutton28 seems to be linked to that unwanted callback (I put a break point in all pushbutton callbacks and this one is caught when pressing the calculate button).
If, in the GUIDE GUI editor, right-click on your open figure and select the Object Browser from the pop-up menu. Look in this list for pushbutton28 (it is near the buttom, in uipanel23). Try selecting it (from the browser) and you should see it appear in the panel (or at least you might see part of the button appear. Delete it, save, and then re-launch your GUI.
Note that I had problems saving the GUI when I deleted the button. Perhaps that is just because of my version of MATLAB (R2041a).