Hi Igor,
I went through all the steps you described.
The one that worked was the last one. I moved the folder where the custom styles and transitions are stored.
I reopened PTE AV Studio and the transition worked. Then, as you said, I deleted the new folder automatically created "Styles and Transitions", and replaced it with my original folder. And then it didn't work again.
I did the same thing again, but instead of completely replacing the new automatically created folder, I kept the newly created ".ini" files and just copied and pasted my other original files.
And it's working for the moment.
Thanks for taking the time to reply.
Georges