Took your advice and got the page running from your suggestions by putting the pop-up above the on-click buttons on the main page (thanks). Everything works fine the first time thru (click on the 'learn more' in the left column, close the resulting pop-up, then click on the topmost 'learn more' in the right column, close, then the third... etc.).
Unfortunately the whole thing falls apart if you then click on the 'learn mores' in almost any random order (easier to ask you to simply try it yourself than to explain the symptoms, since they vary depending on the order you click them - I'm guessing you'll know what's happening pretty quickly).
I've been playing whack-a-mole to try to solve the problem for the past 5 days. It seems suspiciously similar to the initial problem I had, but somehow I'm just not seeing what's wrong now. Again, help appreciated.
The page is at http://gcodisplays.com/content/howRev7.html .
The code for the three 'learn more' buttons is at lines 274, 285, and 295 respectively.
The code for the three 'close window' buttons is at lines 305, 316, 328 respectively.
Again, help appreciated. - Jim