I got fed up with the blank screen so I stopped it and added some diagnostic messages to the main script.

So far I've got this:
code:
Loop #1 @ 09:29:59
   CD #1 @ 09:29:59
   CD #2 @ 09:31:37
   CD #3 @ 09:31:39
   CD #4 @ 09:31:43
   CD #5 @ 09:31:46
It is now 11:42 local time, so CD#5 has taken 2 over 2 hours and hasn't finished wherase the rest of them took no more than a few minutes.
Hmmm. very odd. Best have another look at that code...