Hi Davo, upgraded checklist(from release 20130309 to release 20130424) on different 2.4 sites - 2.4.1, 2.4.3.
1. When I try to add a new aktivity/checklist in a course the only thing i get is a white screen (I would expect the checklist settings dialog)
2. the same problem (white screen) occurs when I try to edit the setting of an already existing checklist

There is no error showing upp
I tried IE, Chrome, Firefox - same result