Unable to open the Custom Animation menu

[PeeWee76]

Because of being unable to open the Custom Animation menu, I tried updating to version 4.1.8 to see if that solved the issue. It did: I was then able to open custom animation and to prepare a presentation and the animation worked fine. I've now returned to the presentation to make some alterations and once again find I cannot open the animation menu. I've tried reinstalling 4.1.8 to no avail. Any help much appreciated.