This is more curiousity than a support issh because there was a simple workaround.
Build is 7/3, OS is XP.
I had added a new screen to my Vista machines and it was time to replicate it on my 1 remaining XP PC.
Vista was fine.
My XP PC refused to add another event to the goto group. It just stared at me. I rebooted, did a cold start, nada.
I tested adding events to other groups with no probs.
So, I just created another event group called goto2. Was able to add the goto screen event to the button with no problem.
Odd.