John,

Many thanks for the response and I appreciate what you are saying.

However, I have now managed to narrow the problem down somewhat and it would appear to be a vba issue. Hopefully the following will clearly explain what is / isn't happening and enable someone to offer a solution.
Courtesy of OfficeOne I am using their EventGenerator add-in and have coded for several events. OnSlideShowBegin and OnSlideShowEnd, both of which interact with two Excel files, are absolutely fine. The problem would appear to be with OnSlideShowNextSlide.
As previously stated I have a one slide presentation set to loop until esc. The extent of the simple PP animation is that shape 'MainBoard' fades in and is visible for 20 seconds before fading out. Then it loops to repeat.
For the past 5 years, using PP2007, the OSSNS event has called a sub, ‘MoveMain’ which grabs some data from an Excel file and then repositions the shape ‘MainBoard’. The slide then redisplays / animates the modified slide and loops again. Since being forced into using PP 2013 the automatic looping is being prevented. Slide change / loop progress can only be made with a click or spacebar hit.
Sadly, I do not have the ability to revert to the old set up, not even for testing.

Reduced down to a simple form, instead of calling ‘MoveMain’ I just tested with a one line reposition, here is the OSSNS event code.

Without calling 'MoveMain' or the test one-liner everything is fine. My watch / debug bits are being processed and the slide keeps auto-looping as required.

With e.g. the one-liner that moves the MainBoard shape the auto-looping stops and a manual click is required to move it on!!!

So my questions would be.
1) Does the OSSNS event not handle 2013 in the same way that it did 2007 ? Which is probably a question I should direct to the good people at OfficeOne?

2) Is there a workaround ? After the call to 'MoveMain' is there some action that I can invoke that will mimic the now required spacebar hit?

Thanks once again for your time and interest.