If the macro fails,  you can't run any macro until you press the
square Reset button on the VBE toolbar.    
  Look like VCR buttons: Run (play) / Break (pause) / Reset (stop)
 You might get a message "can't execute in break mode"

If you have a dialog popup on your Excel  (or even in other software calling
for attention).  It will interfer with working with macros in the VBE.   
   In the VBE all get is a bell each time you depress a key to edit macro 
   or work with menus.   No indicator if sound is turned off.

I've had a problem where one or more toolbar buttons
are blacked out and not available.  I can't duplicate the problem and never
really had a handle on it.  I think I see it when files are being opened at
startup.  Do you see blacked out buttons on the Excel.


Hi Nina,
The  A1:   in front is just a notation that the formula goes
into cell A1  for the example.   The formula split onto
multiple lines you would have to gather it together again.
ExpDate is your date in a another cell or it could be
named range for a cell.

But I think if you look at Chip Pearson's page you would have
a better perspective on the whole mess (MS mess, that is).
  http://www.cpearson.com/excel/datedif.htm